RAID5 for Linux

[richb at pioneer.ci.net (Rich Braun)]

Bob Keyes wrote:
> At my new job, we have a NAS "Snap Appliance", which is pretty
> horrible and I want to get rid of it. So I am going to push for
> a Linux solution. I'd want RAID level 5, and Serial ATA drives,
> and of course linux niceness. I was looking at the Adaptec
> 2810SA, but it's got 8 ports..I though you needed 9 for RAID5
> (one for each bit plus one parity) or am I misunderstanding
> this? I'd also want hot-swappable. Anyone have any suggestions?

I've read through some of the responses and have a couple things to add:

- I think the Snap product *is* Linux-based.  What you're wanting, of course,
is control over the O/S environment in your server.
- You don't say explain what features of the NAS box make it horrible in your
situation, or what level of performance you're lokoing for.
- The stated requirements of serial ATA and hot-swap imply high-end hardware
that will come at a hefty price.  I'm frugal, personally, and generally
question whether high-priced features really fit the bill.  For example,
hot-swap can be justified on a mail server at an ISP but not at most 9-to-5
corporate sites where it's easy enough to shut the system off for 5 minutes at
the end of the workday.  Serial ATA can be justified if you need 15,000rpm
drives because the system is handling 1000 transactions per second in a
banking app, but not if you're running a Clearcase server for a half-dozen VB
programmers.
- A $75 motherboard with a $85 CPU has enough horsepower and IDE ports to run
software RAID1 or RAID5 on four drives in 98% of the environments that I've
seen.
- You don't get any penalty for running RAID1 in software, and you can't get a
performance boost running RAID1 in hardware, on a 2-drive system.  You would
get a performance boost running hardware RAID5 vs. software RAID5, but the
boost may not be measurable if your application is not I/O-bound.

Advances in hardware performance have outraced application requirements in
most situations for a few years now.  Just because a high-end product is
available does not mean it's worth paying the premium.

> For backup, I am thinking the Sony AIT-2 changer, LIB-D81/A2. Don't
> know if it's compatible with Bacula though...

Thumbs up to AIT-2.  I use a Cybernetics/Spectra changer for my AIT-2 drive at
home.  The SCSI standard for changers is widespread:  any brand should work
with any Linux or Windows software.  I use amanda for backups and am
more-or-less happy with it, though I wish it were more popular and were
getting more new features and bug-fixes.

-rich