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Re: LVM on the Slug

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  • johnsinodun
    ... Why is that more of a problem with LVM on the drive than without? If a drive which is in use is disconnected then you re FUBARed whether or not you use
    Message 1 of 9 , Mar 4 11:10 AM
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      --- In nslu2-linux@yahoogroups.com, "Gerald L. Clark"
      <gerald_clark@...> wrote:
      >
      > johnsinodun wrote:
      > > I'm looking at using a slug as an extra file server for Linux clients
      > > and it seems fairly obvious to use LVM for managing the partitions on
      > > the slug.
      > It is not obvious to me.
      > You have very limited memory and flash space.
      > You have USB drives that can be easily connected and disconnected either
      > intentionally or by accident.

      Why is that more of a problem with LVM on the drive than without? If
      a drive which is in use is disconnected then you're FUBARed whether or
      not you use LVM.

      > LVM would be a disaster waiting to happen.
      > What happens if a drive gets disconnected?

      The same as normally happens when a drive is disconnected.

      > You might be ok as long as you don't put more than a single physical
      > volume in a volume group. What then, is the advantage?

      You can change the size of partitions on the fly instead of having to
      decide how much space to allocate to each purpose right at the beginning.

      Once you've got used to the facilities of LVM it's very hard to go
      back to doing things the old-fashioned way.

      John
    • Gerald L. Clark
      ... Internal drives don t get disconnected, unless you are mucking around inside the cabinet while it is running. External drives are succeptable to loose usb
      Message 2 of 9 , Mar 4 3:12 PM
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        johnsinodun wrote:
        > --- In nslu2-linux@yahoogroups.com, "Gerald L. Clark"
        > <gerald_clark@...> wrote:
        >>
        >> johnsinodun wrote:
        >> > I'm looking at using a slug as an extra file server for Linux clients
        >> > and it seems fairly obvious to use LVM for managing the partitions on
        >> > the slug.
        >> It is not obvious to me.
        >> You have very limited memory and flash space.
        >> You have USB drives that can be easily connected and disconnected either
        >> intentionally or by accident.
        >
        > Why is that more of a problem with LVM on the drive than without? If
        > a drive which is in use is disconnected then you're FUBARed whether or
        > not you use LVM.
        >
        >> LVM would be a disaster waiting to happen.
        >> What happens if a drive gets disconnected?
        >
        > The same as normally happens when a drive is disconnected.
        Internal drives don't get disconnected, unless you are mucking around
        inside the cabinet while it is running.
        External drives are succeptable to loose usb connectors, loose power
        connectors etc.

        >
        >> You might be ok as long as you don't put more than a single physical
        >> volume in a volume group. What then, is the advantage?
        >
        > You can change the size of partitions on the fly instead of having to
        > decide how much space to allocate to each purpose right at the beginning.
        This is not an advantage unless you have more than one physical volume
        in a group.
        Separate directories will do almost as well, and have no overhead.
        >
        > Once you've got used to the facilities of LVM it's very hard to go
        > back to doing things the old-fashioned way.
        I have 6 physical drives in a raid, and I use LVM2.
        I don't believe the slug is suitable for use with a large number of
        drives. I doesn't have enough memory for disk cache, and no ecc or parity.
        I would not trust my data to a slug.

        I have run raid 1 on the slug with 2 drives, raiding all 3 partitions.
        I replaced it with an VIA motherboard in a cabinet with 6 drives.
        I would not put more than one drive in a volume group unless they were
        raided.

        I believe the slug is great for tasks like dnsmasq, and that is what my
        slug is currently doing.
        >
        > John
        >
      • johnsinodun
        ... clients ... partitions on ... either ... You seem to be getting very muddled. The issue under discussion is whether or not to use LVM. Whether or not to
        Message 3 of 9 , Mar 4 3:47 PM
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          --- In nslu2-linux@yahoogroups.com, "Gerald L. Clark"
          <gerald_clark@...> wrote:
          >
          > johnsinodun wrote:
          > > --- In nslu2-linux@yahoogroups.com, "Gerald L. Clark"
          > > <gerald_clark@> wrote:
          > >>
          > >> johnsinodun wrote:
          > >> > I'm looking at using a slug as an extra file server for Linux
          clients
          > >> > and it seems fairly obvious to use LVM for managing the
          partitions on
          > >> > the slug.
          > >> It is not obvious to me.
          > >> You have very limited memory and flash space.
          > >> You have USB drives that can be easily connected and disconnected
          either
          > >> intentionally or by accident.
          > >
          > > Why is that more of a problem with LVM on the drive than without? If
          > > a drive which is in use is disconnected then you're FUBARed whether or
          > > not you use LVM.
          > >
          > >> LVM would be a disaster waiting to happen.
          > >> What happens if a drive gets disconnected?
          > >
          > > The same as normally happens when a drive is disconnected.
          > Internal drives don't get disconnected, unless you are mucking around
          > inside the cabinet while it is running.
          > External drives are succeptable to loose usb connectors, loose power
          > connectors etc.

          You seem to be getting very muddled. The issue under discussion is
          whether or not to use LVM. Whether or not to use USB drives is a
          constant. It's pointless to bring up the question of whether internal
          drives would be any less likely to be disconnected, since a) the slug
          can't have internal drives, and b) it isn't relevant to the question
          of whether one can use LVM on an external drive.

          > >> You might be ok as long as you don't put more than a single physical
          > >> volume in a volume group. What then, is the advantage?
          > >
          > > You can change the size of partitions on the fly instead of having to
          > > decide how much space to allocate to each purpose right at the
          beginning.
          > This is not an advantage unless you have more than one physical volume
          > in a group.

          Completely untrue. It can be very useful, given a single large
          physical volume, to allocate space to several purposes and hold back a
          proportion of the space to increase the size of existing chunks at a
          later date if needed.

          > Separate directories will do almost as well, and have no overhead.

          Almost, but not quite. They don't give you the same control over disk
          usage and you can't tune filing system parameters for each purpose.
          What if I want one of my slices to be a Usenet news spool and another
          one to hold MythTV recordings? There's no way that a single partition
          can be formatted to be ideal for both.

          > >
          > > Once you've got used to the facilities of LVM it's very hard to go
          > > back to doing things the old-fashioned way.
          > I have 6 physical drives in a raid, and I use LVM2.
          > I don't believe the slug is suitable for use with a large number of
          > drives.

          Nobody (except you) has suggested using a large number of drives, or
          even more than one drive.

          > I doesn't have enough memory for disk cache, and no ecc or parity.
          > I would not trust my data to a slug.

          What's the point of one then? It's whole raison d'etre is as a data
          storage device.

          You seem to have run away with the idea that I'm proposing a large
          RAID array hanging off a slug, but I've suggested no such thing. All
          I want to do is use LVM to manage the space on one large USB drive.
          You haven't come up with any cogent reasons why I shouldn't do that.

          Cheers,
          John
        • Stanley P. Miller
          I have 3 drives on one of my slugs and getting LVM to work would be nice to have. Now I have to hassle with 3 data directories and trying to remember where I
          Message 4 of 9 , Mar 5 6:02 AM
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            I have 3 drives on one of my slugs and getting LVM to work would be
            nice to have. Now I have to hassle with 3 data directories and trying
            to remember where I put the data I want.

            One big LVM volume would be very handy for my use, especially when I
            fill up and need a 4th, 5th or 6th drive.

            --- In nslu2-linux@yahoogroups.com, "johnsinodun" <yahoo@...> wrote:
            >
            > --- In nslu2-linux@yahoogroups.com, "Gerald L. Clark"
            > <gerald_clark@> wrote:
            > >
            > > johnsinodun wrote:

            <<snip>>

            > Nobody (except you) has suggested using a large number of drives, or
            > even more than one drive.
            >
            > > I doesn't have enough memory for disk cache, and no ecc or parity.
            > > I would not trust my data to a slug.
            >
          • Drew
            ... And I for one think running LVM on a single drive, USB or otherwise, is perfectly fine. Admittedly the rig I use LVM on isn t a slug but the basic concept
            Message 5 of 9 , Mar 5 11:25 AM
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              > You seem to be getting very muddled. The issue under discussion is
              > whether or not to use LVM. Whether or not to use USB drives is a
              > constant. It's pointless to bring up the question of whether internal
              > drives would be any less likely to be disconnected, since a) the slug
              > can't have internal drives, and b) it isn't relevant to the question
              > of whether one can use LVM on an external drive.

              And I for one think running LVM on a single drive, USB or otherwise,
              is perfectly fine.

              Admittedly the rig I use LVM on isn't a slug but the basic concept is
              the same. My rig uses an 80 and a 120GB drive with the 80GB drive
              mirrored against an 80GB partition. The RAID-1 partition is LVM'd and
              is used to support several file systems based on my (changing) usage.
              The remaining 40GB is split between three partitions, two used for
              core system files and one large LVM partition that holds everything
              else.


              -Drew
            • Brian Wood
              ... I ve been following this thread and have a question, how much CPU overhead does LVM have ?? I ve seen folks on the MythTV lists complain about the LVM
              Message 6 of 9 , Mar 5 3:13 PM
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                On Mar 5, 2006, at 12:25 PM, Drew wrote:

                > > You seem to be getting very muddled. The issue under discussion is
                > > whether or not to use LVM. Whether or not to use USB drives is a
                > > constant. It's pointless to bring up the question of whether
                > internal
                > > drives would be any less likely to be disconnected, since a) the
                > slug
                > > can't have internal drives, and b) it isn't relevant to the
                > question
                > > of whether one can use LVM on an external drive.
                >
                > And I for one think running LVM on a single drive, USB or otherwise,
                > is perfectly fine.
                >
                > Admittedly the rig I use LVM on isn't a slug but the basic concept is
                > the same. My rig uses an 80 and a 120GB drive with the 80GB drive
                > mirrored against an 80GB partition. The RAID-1 partition is LVM'd and
                > is used to support several file systems based on my (changing) usage.
                > The remaining 40GB is split between three partitions, two used for
                > core system files and one large LVM partition that holds everything
                > else.
                >
                >
                > -Drew
                >
                >
                I've been following this thread and have a question, how much CPU
                overhead does LVM have ??

                I've seen folks on the MythTV lists complain about the LVM overhead,
                and that is on machines that can handle multiple HD video streams, so
                I would suspect that the one-lung CPU in the Slug would be severely
                taxed.

                Given the already slow hard disk performance of the slug, it seems to
                me that the last thing you would want to do would be to slow it down
                any more unless you had absolutely no other choice.
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