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Re: ISCSI - does it work?

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  • Charles Lindsey
    ... So yes, we seem to agree on the level that its a neat and useful concept, but maybe the actual implementation will turn out to be a bad match. ... I have
    Message 1 of 8 , Jul 7, 2009
      --- In nslu2-linux@yahoogroups.com, "Mike Westerhof (mwester)" <mwester@...> wrote:
      > Charles Lindsey wrote:
      > > --- In nslu2-linux@yahoogroups.com, "Mike Westerhof (mwester)" <mwester@> wrote:

      > >> The nature and intention of iscsi is so contrary to what the NSLU2 can
      > >> do that nobody has ever tried what you wish to do. That's not to say
      > >> that it can't be done -- just to note that you'll be the pioneer blazing
      > >> a trail that few, if any, will follow ;-)
      > >
      > > But I am surprised you say that. Surely the purpose of the NSLU2 is to access assorted devices across the network, and surely making it appear that the device is actually on your own machine is the ultimate solution to that problem?
      > It's an opinion; feel free to differ. But for what it's worth, here's
      > my thinking on the issue:

      > Now ISCSI: the concept also matches the NSLU2 very well. It doesn't
      > work very well with Windows (yet), but the big conceptual "win" over NFS
      > is block-level access to a device over the network. Cool. I can't
      > speak to the "protocol/architecture" - I have a feeling that while the
      > security aspects may be heavy-weight, the actual data-moving part of the
      > protocol is probably well-suited to *nix systems (contrasting with the
      > Windows/SMB/Samba model which does not fit very well at all, resulting
      > in significant protocol overhead for some operations). Unfortunately,
      > from what I've been able to determine, the "implementation" side of
      > things for ISCSI is not a great fit -- it's huge, relies on lots of
      > large libraries, and expects much infrastructure from the host. Rather
      > like the latest Samba packages, as a matter of fact!

      So yes, we seem to agree on the level that its a neat and useful concept, but maybe the actual implementation will turn out to be a bad match.
      > Digging into the ISCSI stuff more deeply, I was unable to get it to work
      > at all on my Fedora host - too much stuff, too many dependencies, too
      > much setup.

      I have no experience of actually using ISCSI, but it seems that my present host has all the necessary handles ready to be used.

      > So, my conclusion is that ISCSI is a conceptual match for the NSLU2 and
      > similar devices, but that it's not a practical match (yet) due to the
      > lack of "tiny host" or "essential" server package. If the on-the-wire
      > protocol turns out to be light-weight enough (i.e. does not require gobs
      > of RAM to cache data or maintain in-memory tables, etc.), it might turn
      > out to be a great way to access remote devices.

      Yes, that RAM usage might be the killer. But I have no evidence either way as yet.
      > But another consideration is that ISCSI provides only block-level access
      > to the device on the server -- that precludes sharing. It also
      > precludes filesystem-transparency. These are things that Samba and NFS
      > provide, instead. If you're ok with that, then basically what it comes
      > down to is that you are using the NSLU2 as a "USB extender", right?

      Right indeed.That is just what my Slug is intended to be (no other users on the network to get in the way).

      > Finally, I'll mention that there is a package (don't recall the name
      > right now) that does "ATA-over-ethernet" -- basically this is like a
      > loopback filesystem that works over the network.

      Yes, I was aware that solutions of that nature would be possible, but not aware of actual implementations. Any further information you could give would be welcome, especially if it has already been tried on 4.8.
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