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postfix clustering

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  • Low Kian Seong
    Dear all, I know this question has probably been asked before, but are there any resources out there on doing postfix clustering or replication ? Sorry for
    Message 1 of 18 , Apr 1, 2007
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      Dear all,

      I know this question has probably been asked before, but are there any resources out there on doing postfix clustering or replication ?

      Sorry for asking a noobie question and thanks in advanced.



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    • Adrian Ulrich
      ... What problem are you trying to solve? - Distributing load? - A HA-Mail-Queue? - ... ? Regards, Adrian
      Message 2 of 18 , Apr 2, 2007
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        > I know this question has probably been asked before, but are there any resources out there on doing postfix clustering or replication ?

        What problem are you trying to solve?

        - Distributing load?
        - A HA-Mail-Queue?
        - ... ?

        Regards,
        Adrian
      • Peter
        Hello, I want to use postfix for active/active mode. Here is my dns settings: mycompany.com MX 10 first.mycompany.com mycompany.com MX 10 second.mycompany.com
        Message 3 of 18 , Oct 28, 2010
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          Hello,

          I want to use postfix for active/active mode.

          Here is my dns settings:

          mycompany.com MX 10 first.mycompany.com
          mycompany.com MX 10 second.mycompany.com


          "first" and "second" machine are located in the different physical location

          I have two issues here:

          1) where should I point my pop server?
          If I point to first.mycompany.com, any mails received in second.mycompany.com cannot be viewed?

          2) is there a better way to synchronize the mails in first and second mail server? it will be good if one server is down and there is no disruption.

          I checked the documentation regarding the setup for postfix for multiple mx records, but I am not sure how these two problems can be solved.

          thanks a lot for the help in advance.

          Peter
        • Victor Duchovni
          ... No, you want to cluster your mailstore (IMAP, POP, ...). This is not Postfix. Multiple Postfix MX hosts do not need to be clustered, the SMTP design
          Message 4 of 18 , Oct 28, 2010
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            On Thu, Oct 28, 2010 at 11:41:17AM -0700, Peter wrote:

            > I want to use postfix for active/active mode.

            No, you want to cluster your mailstore (IMAP, POP, ...). This is not
            Postfix. Multiple Postfix MX hosts do not need to be clustered, the
            SMTP design automatically load-balances multiple MX hosts.

            In an HA environment, your front-end SMTP servers would not be where
            you store your mail, rather the clustered IMAP servers would be behind
            the MX hosts, which are not clustered.

            Designing a clustered mail store is an interesting problem, but really
            a Postfix issue.

            --
            Viktor.
          • Peter
            Hi Victor, thanks for your response. ... That is true. It might be easy if two mail server (with MX record) are located in the same physical location. We can
            Message 5 of 18 , Oct 28, 2010
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              Hi Victor,

              thanks for your response.

              > > I want to use postfix for active/active mode.
              >
              > No, you want to cluster your mailstore (IMAP, POP, ...).
              > This is not
              > Postfix. Multiple Postfix MX hosts do not need to be
              > clustered, the
              > SMTP design automatically load-balances multiple MX hosts.

              That is true. It might be easy if two mail server (with MX record) are located in the same physical location. We can use a different server (imap store) or shared storage for storing the mails for two mail servers.

              but if the mail servers are located in a different location, it will be hard to maintain such a shared mailstore.

              Peter
            • Stan Hoeppner
              ... I think Victor meant not a Postfix issue. If you want to build a mail store cluster over a WAN link, start your reading here: http://www.drbd.org
              Message 6 of 18 , Oct 28, 2010
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                Victor Duchovni put forth on 10/28/2010 2:00 PM:
                > On Thu, Oct 28, 2010 at 11:41:17AM -0700, Peter wrote:
                >
                >> I want to use postfix for active/active mode.
                >
                > No, you want to cluster your mailstore (IMAP, POP, ...). This is not
                > Postfix. Multiple Postfix MX hosts do not need to be clustered, the
                > SMTP design automatically load-balances multiple MX hosts.
                >
                > In an HA environment, your front-end SMTP servers would not be where
                > you store your mail, rather the clustered IMAP servers would be behind
                > the MX hosts, which are not clustered.
                >
                > Designing a clustered mail store is an interesting problem, but really
                > a Postfix issue.

                I think Victor meant "not" a Postfix issue. If you want to build a mail
                store cluster over a WAN link, start your reading here:

                http://www.drbd.org
                http://sourceware.org/cluster/gfs/

                The combination of these will allow you to accomplish your cluster goal.
                Depending on the aggregate write bandwidth of your MTAs and delete b/w
                of your POPD, you may need a site-to-site link of anywhere from 10Mb/s
                to 100Mb/s, or maybe even more. If your two servers are located in
                buildings on the same campus and connected via 100/1000Mb/s ethernet
                then this solution will work very well. If your two servers are located
                in two internet colocation facilities and your b/w is limited to 10Mb/s
                or less, RTTs are unstable, etc, then this solution may not work well
                for you. Mirroring a disk over a network requires a stable quality network.

                If your network is stable and the bandwidth sufficient, this is the way
                you want to cluster across a network. If you lack the network
                prerequisites, you're not going to be able to effectively implement an
                active/active cluster with the solution above or any other.

                --
                Stan
              • Peter
                Hi Stan, ... I agree with your point. the above solution should work well if the active/active server are located in the same location. for the machines in
                Message 7 of 18 , Oct 29, 2010
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                  Hi Stan,


                  >
                  > I think Victor meant "not" a Postfix issue.  If you
                  > want to build a mail
                  > store cluster over a WAN link, start your reading here:


                  >
                  > http://www.drbd.org
                  > http://sourceware.org/cluster/gfs/
                  >
                  > The combination of these will allow you to accomplish your
                  > cluster goal.
                  > Depending on the aggregate write bandwidth of your MTAs
                  > and delete b/w
                  > of your POPD, you may need a site-to-site link of anywhere
                  > from 10Mb/s
                  > to 100Mb/s, or maybe even more.  If your two servers
                  > are located in
                  > buildings on the same campus and connected via 100/1000Mb/s
                  > ethernet
                  > then this solution will work very well.  If your two
                  > servers are located
                  > in two internet colocation facilities and your b/w is
                  > limited to 10Mb/s
                  > or less, RTTs are unstable, etc, then this solution may not
                  > work well
                  > for you.  Mirroring a disk over a network requires a
                  > stable quality network.

                  I agree with your point.
                  the above solution should work well if the active/active server
                  are located in the same location.

                  for the machines in different data center, there is no guarantee of speed.

                  also, making the server run in a different data center is fail-over protection solution.

                  using rsync is a way to synchronize the storage.
                  however, multiple MX record only works well if pointing to servers
                  in the same data center sharing the same storage for imap.

                  thus, a valid solution is to change the IP address of imap server
                  when failover is required. but the dns propergation might take up
                  to three days. is there a better alternative?


                  guess it is something beyond postfix to handle. not sure how postfix users will handle such an issue?

                  Thanks.

                  Peter
                • Stan Hoeppner
                  ... Attempting to architect your remote site cluster or failover solution via back-n-forth to the Postfix mail list is not the proper way to go about this. We
                  Message 8 of 18 , Oct 29, 2010
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                    Peter put forth on 10/29/2010 1:55 PM:

                    > guess it is something beyond postfix to handle. not sure how postfix users will handle such an issue?

                    Attempting to architect your remote site cluster or failover solution
                    via back-n-forth to the Postfix mail list is not the proper way to go
                    about this. We can give you pointers, but we can't architect the
                    solution for you. There are too many variables and too much complexity
                    involved, and the solution will be specific to your individual
                    situation, of which providing us all the necessary details would be
                    nearly impossible in this format.

                    It seems you are in over your head and aren't grasping some of the basic
                    principles of Disaster Avoidance and Recovery 101. For instance, cheap
                    and reliable are usually mutually exclusive when it comes to ISPs/Colos.
                    If your remote link is not reliable, then rsync will be no more
                    reliable than DRBD, true?

                    It's probably time to bring in a paid consultant to help you architect
                    this. If you can't afford one, then you really can't afford a good off
                    site resiliency solution. If this is the case, then you should
                    seriously consider outsourced email hosting which will give you all of
                    what you want, albeit with possibly a little less control.

                    --
                    Stan
                  • Wietse Venema
                    ... You are looking for a two-way replicated message store. Postfix is an MTA. Postfix is not a storage manager. Two-way storage replication is a commodity
                    Message 9 of 18 , Oct 30, 2010
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                      Peter:
                      > guess it is something beyond postfix to handle. not sure how postfix
                      > users will handle such an issue?

                      You are looking for a two-way replicated message store. Postfix is
                      an MTA. Postfix is not a storage manager.

                      Two-way storage replication is a commodity solution if the systems
                      are connected by a high-speed interconnect (examples of this are
                      RAID in hardware or software).

                      Two-way storage replication becomes non-trivial if the systems are
                      connected by a wide-area network. That is a specialized niche that
                      few Postfix users will have experience with (I certainly don't).

                      For example you get massive file system corruption when you simply
                      mount an ext4fs-over-drbd file system on two active hosts. Instead,
                      you need to use a file system that is explicitly built for concurrent
                      updates by different hosts (GFS, OCFS and the like).

                      Even a replicated distributed file system will get into trouble
                      when the two sites become isolated from each other, but they keep
                      receiving mail. Those file system updates are likely to conflict
                      with each other.

                      Wietse
                    • Reinaldo de Carvalho
                      ... From Cyrus mailling list: Now that Cyrus 2.4 has been released with a lot of the groundwork for bandwidth efficient replication in place, Max is going to
                      Message 10 of 18 , Oct 30, 2010
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                        On Sat, Oct 30, 2010 at 11:44 AM, Wietse Venema <wietse@...> wrote:
                        Peter:
                        > guess it is something beyond postfix to handle. not sure how postfix
                        > users will handle such an issue?

                        You are looking for a two-way replicated message store. Postfix is
                        an MTA. Postfix is not a storage manager.



                        From Cyrus mailling list:

                        "Now that Cyrus 2.4 has been released with a lot of the groundwork for
                        bandwidth efficient replication in place, Max is going to be working
                        on improving the management tools and monitoring of the replication
                        process.  Our goal is to support master-master replication with safe
                        conflict resolution, and multiple replication topologies including
                        replication with more than two copies.  This will allow efficient
                        failover within a single datacentre as well as geographically
                        distant close-to-real-time disaster recovery."


                        --
                        Reinaldo de Carvalho
                        http://korreio.sf.net
                        http://python-cyrus.sf.net

                        "While not fully understand a software, don't try to adapt this software to the way you work, but rather yourself to the way the software works" (myself)

                      • Stan Hoeppner
                        ... Interesting. This is a _huge_ leap in capability for any IMAP server I m aware of. Yet, entering either replication or cluster in the Cyrus home page
                        Message 11 of 18 , Oct 30, 2010
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                          Reinaldo de Carvalho put forth on 10/30/2010 3:39 PM:

                          > From Cyrus mailling list:
                          >
                          > "Now that Cyrus 2.4 has been released with a lot of the groundwork for
                          > bandwidth efficient replication in place, Max is going to be working
                          > on improving the management tools and monitoring of the replication
                          > process. Our goal is to support master-master replication with safe
                          > conflict resolution, and multiple replication topologies including
                          > replication with more than two copies. This will allow efficient
                          > failover within a single datacentre as well as geographically
                          > distant close-to-real-time disaster recovery."

                          Interesting. This is a _huge_ leap in capability for any IMAP server
                          I'm aware of. Yet, entering either "replication" or "cluster" in the
                          Cyrus home page search box returns zero results. When will these
                          features be released as production ready? Right now it appears they are
                          vaporware.

                          --
                          Stan
                        • Stan Hoeppner
                          ... Correct. ... Correct. ... This statement above is why I m replying a second time to this message. I have two critical questions regarding the apparent need
                          Message 12 of 18 , Oct 30, 2010
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                            Peter put forth on 10/29/2010 1:55 PM:

                            > I agree with your point.
                            > the above solution should work well if the active/active server
                            > are located in the same location.

                            Correct.

                            > for the machines in different data center, there is no guarantee of speed.

                            Correct.

                            > also, making the server run in a different data center is fail-over protection solution.

                            This statement above is why I'm replying a second time to this message.
                            I have two critical questions regarding the apparent need for multi
                            site failover.

                            1. What are your specific failure concerns with your primary site?
                            Network failure? Host failure? Storage hardware failure?

                            2. Individual hosts can be made to me extremely reliable today both at
                            the hardware and software level. And with VMware ESX, for example, two
                            physical hosts, two virtual guests, connected to fully redundant storage
                            (SAN RAID with dual controllers, PSUs, etc) gives you total
                            active/active and/or active/passive failover depending on how you set it
                            up. Even with a single guest server, if one physical host dies, VMware
                            HA will automatically boot the downed guest on the remaining ESX host in
                            a matter of seconds. If you want active/active failover you simply run
                            two guests as an IMAP cluster with a shared SAN LUN formatted with GFS2.
                            Though really, if you have ESX and the hardware setup I mention,
                            there's little need to build a cluster atop it. The only thing a
                            cluster in this scenario might help is if you had massive corruption of
                            the root filesystem of one of the two IMAP server guests causing it to
                            go down.

                            3. With the hardware/software failure modes covered in #2, your only
                            remaining concern is network availability. In this case, simply have
                            another (backup) internet connection installed at your facility,
                            preferably from a different provider.

                            You could choose to use a FLOSS solution instead of VMware ESX and
                            possibly get the same results for less money. I'm not familiar with
                            whether or not the FLOSS hypervisors offer anything like Vmotion and HA.
                            They probably do by now.


                            Maybe a good question for you to ask of the members of this list at this
                            point is:

                            How many OPs here run with a multi site IMAP cluster setup with a
                            physically distributed mail store, either via replication or a cluster
                            filesystem over a wide area network?

                            The answers you get may be quite enlightening.

                            --
                            Stan
                          • Reinaldo de Carvalho
                            ... Cyrus 2.3 already replication support. Join cyrus mailling list. This is off-topic here. -- Reinaldo de Carvalho http://korreio.sf.net
                            Message 13 of 18 , Oct 31, 2010
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                              On Sun, Oct 31, 2010 at 2:13 AM, Stan Hoeppner <stan@...> wrote:
                              Reinaldo de Carvalho put forth on 10/30/2010 3:39 PM:

                              > From Cyrus mailling list:
                              >
                              > "Now that Cyrus 2.4 has been released with a lot of the groundwork for
                              > bandwidth efficient replication in place, Max is going to be working
                              > on improving the management tools and monitoring of the replication
                              > process.  Our goal is to support master-master replication with safe
                              > conflict resolution, and multiple replication topologies including
                              > replication with more than two copies.  This will allow efficient
                              > failover within a single datacentre as well as geographically
                              > distant close-to-real-time disaster recovery."

                              Interesting.  This is a _huge_ leap in capability for any IMAP server
                              I'm aware of.  Yet, entering either "replication" or "cluster" in the
                              Cyrus home page search box returns zero results.  When will these
                              features be released as production ready?  Right now it appears they are
                              vaporware.


                              Cyrus 2.3 already replication support. Join cyrus mailling list. This is off-topic here.


                              --
                              Reinaldo de Carvalho
                              http://korreio.sf.net
                              http://python-cyrus.sf.net

                              "While not fully understand a software, don't try to adapt this software to the way you work, but rather yourself to the way the software works" (myself)

                            • Peter
                              Hi Stan, ... You have a great suggestion assuming the data center functions well. the data center primary site failure means that the data center itself
                              Message 14 of 18 , Nov 1, 2010
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                                Hi Stan,

                                > 1.  What are your specific failure concerns with your
                                > primary site?
                                > Network failure?  Host failure?  Storage hardware
                                > failure?

                                You have a great suggestion assuming the data center functions well.

                                the data center primary site failure means that the data center
                                itself failed, meaning the host machine/storage/network are all in-accessible.






                                > Maybe a good question for you to ask of the members of this
                                > list at this
                                > point is:
                                >
                                > How many OPs here run with a multi site IMAP cluster setup
                                > with a
                                > physically distributed mail store, either via replication
                                > or a cluster
                                > filesystem over a wide area network?
                                >

                                That is a good question. It is something I am looking for.

                                however, if not going for expensive cluster filesystem over a wide area network,
                                one simple way is to rsync every 5 minutes to copy over a backup serer in another data center and a quick
                                dns change if the primary data center failed. The TTL in DNS settings can be 5 minutes.


                                Peter
                              • Stan Hoeppner
                                ... You seem to be looking at this from a macro point of view. For an entire datacenter to fail you re looking at something like a natural disaster
                                Message 15 of 18 , Nov 1, 2010
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                                  Peter put forth on 11/1/2010 6:51 PM:
                                  > Hi Stan,
                                  >
                                  >> 1. What are your specific failure concerns with your
                                  >> primary site?
                                  >> Network failure? Host failure? Storage hardware
                                  >> failure?
                                  >
                                  > You have a great suggestion assuming the data center functions well.
                                  >
                                  > the data center primary site failure means that the data center
                                  > itself failed, meaning the host machine/storage/network are all in-accessible.

                                  You seem to be looking at this from a macro point of view. For an
                                  entire datacenter to "fail" you're looking at something like a natural
                                  disaster (hurricane, earthquake, tornado, flood, lightning) destroying
                                  the facility, or all power and comm lines into it. The probability of
                                  these things is very low, assuming the datacenter was located, designed,
                                  and constructed properly.

                                  I suggest you need to look at disaster avoidance and recovery from a
                                  micro point of view. Failures at the micro level are far more common,
                                  and less expensive to architect around and recover from.

                                  >> Maybe a good question for you to ask of the members of this
                                  >> list at this
                                  >> point is:
                                  >>
                                  >> How many OPs here run with a multi site IMAP cluster setup
                                  >> with a
                                  >> physically distributed mail store, either via replication
                                  >> or a cluster
                                  >> filesystem over a wide area network?
                                  >>
                                  >
                                  > That is a good question. It is something I am looking for.

                                  Then simply start a new thread and ask the question of the members of
                                  this list. The answers you get should be very instructive. My guess is
                                  that very very few OPs here are doing what you're attempting to do, and
                                  yet they have great reliability. I may be all wrong. Ask the list and
                                  get consensus on how others approach disaster avoidance and recover of
                                  their IMAP stores.

                                  > however, if not going for expensive cluster filesystem over a wide area network,
                                  > one simple way is to rsync every 5 minutes to copy over a backup serer in another data center and a quick
                                  > dns change if the primary data center failed. The TTL in DNS settings can be 5 minutes.

                                  This is not automatic fail over. If you're going to bother with a
                                  remote hot site, you should have automatic fail over of the mailbox server.

                                  Again, I ask you, is your primary site so prone to failure that you
                                  _need_ a remote site? Let me guess: You have already sold your
                                  superiors on the idea of a remote hot site, and now you're trying to
                                  figure out how to implement it?

                                  If this is the case I'm wasting my breath and you are wasting the lists'
                                  time. A technical engineer identifies a problem and then finds and
                                  implements the proper solution. He doesn't pick a solution from a
                                  magazine article or blog that sounds neat, to a problem that may or may
                                  not exist at his organization, and then drive to implement it due to
                                  personal desires instead of operational needs.

                                  A hot backup site is actually relatively rare. Few organizations
                                  implement this strategy. In the vast majority of cases the cost of such
                                  an architecture (hardware, comms links, testing, admin time, etc)
                                  outweighs the benefit due to reliability of the primary site and thus
                                  the fact the hot site is rarely if ever used.

                                  Ask the members of this list how many do IMAP store replication/fail
                                  over to a remote site.

                                  --
                                  Stan
                                • Mark Scholten
                                  ... It sounds interesting, however from a system administrator point of view it shouldn t be really difficult to create with the current tools. With some
                                  Message 16 of 18 , Nov 2, 2010
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                                    > -----Original Message-----
                                    > From: owner-postfix-users@... [mailto:owner-postfix-
                                    > users@...] On Behalf Of Stan Hoeppner
                                    > Sent: Sunday, October 31, 2010 6:14 AM
                                    > To: postfix-users@...
                                    > Subject: Re: postfix clustering
                                    >
                                    > Reinaldo de Carvalho put forth on 10/30/2010 3:39 PM:
                                    >
                                    > > From Cyrus mailling list:
                                    > >
                                    > > "Now that Cyrus 2.4 has been released with a lot of the groundwork
                                    > for
                                    > > bandwidth efficient replication in place, Max is going to be working
                                    > > on improving the management tools and monitoring of the replication
                                    > > process. Our goal is to support master-master replication with safe
                                    > > conflict resolution, and multiple replication topologies including
                                    > > replication with more than two copies. This will allow efficient
                                    > > failover within a single datacentre as well as geographically
                                    > > distant close-to-real-time disaster recovery."
                                    >
                                    > Interesting. This is a _huge_ leap in capability for any IMAP server
                                    > I'm aware of. Yet, entering either "replication" or "cluster" in the
                                    > Cyrus home page search box returns zero results. When will these
                                    > features be released as production ready? Right now it appears they
                                    > are
                                    > vaporware.

                                    It sounds interesting, however from a system administrator point of view it
                                    shouldn't be really difficult to create with the current tools. With some
                                    custom scripts I think it should be possible to do it with current tools,
                                    the most difficult part is messages that get deleted from the file system
                                    (pop3/imap) I guess.

                                    I can set it up later this year in a test environment and publish my
                                    findings about it. If this is interesting for others to know please mention
                                    it and I'll test it and publish it.

                                    Regards, Mark
                                  • Peter
                                    - ... I am a little surprised about your common sense for the data protection. obviously, you never heard of data center on fire that wipes out all servers or
                                    Message 17 of 18 , Nov 2, 2010
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                                      -
                                      > > Hi Stan,
                                      > >
                                      > >> 1.  What are your specific failure concerns
                                      > with your
                                      > >> primary site?
                                      > >> Network failure?  Host failure?  Storage
                                      > hardware
                                      > >> failure?
                                      > >
                                      > > You have a great suggestion assuming the data center
                                      > functions well.
                                      > >
                                      > > the data center primary site failure means that the
                                      > data center
                                      > > itself failed, meaning the host
                                      > machine/storage/network are all in-accessible.
                                      >
                                      > You seem to be looking at this from a macro point of
                                      > view.  For an
                                      > entire datacenter to "fail" you're looking at something
                                      > like a natural
                                      > disaster (hurricane, earthquake, tornado, flood, lightning)
                                      > destroying
                                      > the facility, or all power and comm lines into it. 
                                      > The probability of
                                      > these things is very low, assuming the datacenter was
                                      > located, designed,
                                      > and constructed properly.

                                      I am a little surprised about your common sense for the data protection.

                                      obviously, you never heard of data center on fire that wipes out
                                      all servers or all servers were down for 3 or more days.

                                      Just a quick google search and there are so many data centers related
                                      issue reported in the past.

                                      http://www.thetechherald.com/article.php/200823/1124/The-Planet-Outage-%E2%80%93-H1-Datacenter-suffers-fire-and-explosion-Update-1

                                      http://www.techflash.com/seattle/2009/07/Why_the_Seattle_data_center_fire_caught_companies_unprepared49978502.html

                                      http://www.datacenterknowledge.com/archives/2008/03/31/fire-destroys-wisconsin-data-center/

                                      http://www.intology.com/computers-internet/us-data-center-catches-fire-9000-servers-down/

                                      http://www.prisontalk.com/forums/showthread.php?t=340505

                                      anyway, thanks for your other suggestions.

                                      Peter
                                    • Peter
                                      ... it is great if you can create a blog to share. Thanks, Peter
                                      Message 18 of 18 , Nov 2, 2010
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                                        > > Interesting.  This is a _huge_ leap in capability
                                        > for any IMAP server
                                        > > I'm aware of.  Yet, entering either "replication"
                                        > or "cluster" in the
                                        > > Cyrus home page search box returns zero results. 
                                        > When will these
                                        > > features be released as production ready?  Right
                                        > now it appears they
                                        > > are
                                        > > vaporware.
                                        >
                                        > It sounds interesting, however from a system administrator
                                        > point of view it
                                        > shouldn't be really difficult to create with the current
                                        > tools. With some
                                        > custom scripts I think it should be possible to do it with
                                        > current tools,
                                        > the most difficult part is messages that get deleted from
                                        > the file system
                                        > (pop3/imap) I guess.
                                        >
                                        > I can set it up later this year in a test environment and
                                        > publish my
                                        > findings about it. If this is interesting for others to
                                        > know please mention
                                        > it and I'll test it and publish it.

                                        it is great if you can create a blog to share.

                                        Thanks,

                                        Peter
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