On Aug 17, 2011, at 6:09 AM, Aram Hăvărneanu wrote:

> What's the best option for RAID in Plan9? I understand I can use
> either Ken's fileserver or the Plan9 '#k' device. 

note that neither of these are RAID in the way most people expect. failure
notification, in particular, can be lacking, and they're more restricted in what
they try to do that many RAID systems. that said, I've used #k quite happily for
years with no issues (and periodic correctness checks).

i'm not sure what support, if any, we have for hardware RAID controllers other
than ones which present a single logical disk. those, though, should be an
option if you're concerned.

> Can anyone shed some light on why I might want one and not the other?
> Are there any other options?

ken's fs is a kernel, and essentially gives you a 9p-accessible file storage
appliance. it takes another box to be able to run it. #k is part of the standard
cpu server kernel, and is typically used in conjunction with fossil and/or
venti. really, you usually want to decide between Ken's fs and fossil (with or
without venti). the basics:

Ken's FS used to be the default file server in Plan 9. It's a kernel, and takes over
a box. It is only directly accessible via 9p and il, which pretty much means via
Plan 9 (cpu servers can share the resources as they like, of course). It does
automatic daily archives of the whole system. It does limited de-duplicating.
It is very fast and extremely stable.

fossil is a newer file server, designed for use with venti (but usable on its own,
as well). it can be configured to do daily archives and/or periodic ephemeral
snapshots (you pick how often and how long they last). It can be used stand-
alone (can't do archives that way, but can still do snapshots) or with venti, in
which case you get venti's block-level deduplication (and direct access to
block-level storage). fossil performs reasonably and is relatively stable, but
less so than ken's fs (and, personally, seems more sensitive to unexpected
shutdown). venti is very stable. typically, if fossil goes belly-up, you can
reconstruct it from venti (in every case i've seen).

personally, if you (a) have the extra box to spare, (b) can put in a little extra
work up front, (c) don't care about direct access to block-level storage, and
(d) can live without ephemeral snapshots, i'd suggest ken's fs; otherwise, i'd
suggest fossil backed by venti.

(note that (d) above is slightly tricky, as the ephemeral snapshots in fossil
seem to trigger a bug that causes fossil to hang periodically; most reports
have that happening every ~2 months or so)

this gets asked often, and is worth a wiki page.

> Do you recommend fossil+venti or kfs? I've seen that a lot of people prefer kfs.

note that "kfs", confusingly, is not "ken's fs". that's sometimes (more confusingly)
informally called "kenfs". kfs is a quite old offshoot that used to be the standard
install on things like laptops or other stand-alone systems before fossil came
along.

of kenfs, kfs, and fossil (with or without venti), kfs is your most "traditional" file
system. no snapshots or archives, no connection to venti or similar, no block or
file level de-duplicating. it still has a place, but doesn't sound like what you want.

> Are there any options for block level encryption on Plan9?

there have been a handful of such experiments, but i'm pretty sure there's nothing
in the stock distribution. check the 9fans archives for discussion of the various
experiments. i'm not sure if any were quite "there" yet.

> Is 9p suitable for this? How will the 40ms latency affect 9p operation?

i expect that'll be well low enough for most uses.

> I assume there are no good 9p drivers for Windows so I can
> access my data directly.

there was at least one good one, but (last i checked) it's not generally available
(search the archives for "rangboom" for more info).

> How good are the various
> Plan9 SMB servers? (On the long term I might write a 9p filesystem
> driver for Windows, I've been a Windows filesystem developer in a past
> life). Is it better if I use the Plan9 boxen only for AoE with a Linux
> on top that serves SMB?

i've used the plan9 smb stuff only lightly, but it's worked well for me. there are
folks actively paying attention to it and interested in having it work well, which
is always good. he linux stuff will doubtless be more well-tested, but then you
(a) have an extra layer of stuff to set up and configure, and (b) have linux.

i'd give the plan9 smb stuff a shot and see how it works for you.

> Are there some kind of external enclosures that can hold a reasonable
> number of drives and connect via eSATA or something? Are they fast enough?

"fast enough" depends on your needs. you've said you're on 100Mbit, though, so
i'd expect most decent eSATA enclosures to be fast enough to saturate that link.

i have no recommendations on specific enclosures.

anthony