[SunRescue] Re: Software raid

[Greg A. Woods]

[ On Saturday, March 24, 2001 at 05:31:57 (-0800), Robert Novak wrote: ]
> Subject: [SunRescue] Re: Software raid
>
> I thought I heard a "Joshua D. Boyd" say:
> > 
> > Has anyone here ever tried running software raid-5?  I need a new file
> > server I guess (my current PeeCee one doesn't have enough drive bays or
> > PCI slots).  Sun is an option, but PC is more likely.  
> 
> I've used Solstice Disksuite for RAID on Solaris, and it functions for
> RAID-5, but does not perform too well. Of course I was building it up for
> a higher demand environment than your typical home system (100 software
> developers) so the hits I saw were more profound.

Hmmm...

I hate to say it in this context, but if you want a fairly reliable
RAID-based solution fileserver using RAID-5 for "home" then your best
bet is NetBSD with it's built-in RAIDframe support and a reasonably
recent Intel-based server.  As a file server most any recent PC will
have oodles and oodles of spare CPU for doing the RAID-5 stuff.  You
just cannot beat the Intel-based price/performance ratios these days, at
least not if you're talking only about raw CPU power (though a high-end
Macintosh G4, which will also run NetBSD, will give it a run for your
money too!).

My colleague has a 60GB RAID-5 array on a basic Pentium-III machine with
733MHz CPU that's got Symbios 53c857 ultra-wide PCI controller and 5
decent 17GB drives in an old Compaq hot-swap chassis (maybe $50-100 if
you look around).  The machine has 128 MB of RAM (pretty much standard
for such machines these days).  He boots it off an internal IDE drive
right now but plans to have a pair of mirrored root drives (which NetBSD
can then boot from).

The only problem's been that for reliability's sake you must run the
parity check/rebuild after a crash and *before* you run fsck, and that
takes upwards of two hours on this machine (and with flakey Asus
motherboards crashes are more frequent than desired! :-).

However with NetBSD-1.5 you get full hot-swap support in RAID-5 with a
hot spare (the 5'th drive).  So it's an extremely reliable storage
solution if you happen to pick a reliable motherboard (I'd only ever
recommend a true server, eg. IBM xSeries, or Intel motherboard/server,
but there goes your price/perf ratio....)

It's a relatively good performer too:  ~4MB/s writes and ~16MB/s reads
when just creating and reading a big file in the filesystem from/to
/dev/{zero,null}.

If I can ever find a beefy enough PS/2-AT power supply I'm going to try
the same on a Sparc-20 SM71 with four old 2GB 5.25" drives (and just not
worry about the hot-swap spare :-)....  I doubt my sparc-2 would be able
to keep even the internal SCSI bus running fast enough and do RAID-5
though.  (It needs to be about a 400W PS/2-AT power supply because
that's all that'll fit in the Trimm chassis I have, and four of these
drives need more than 14A @ 12vdc just to keep three spinning while the
fourth starts up and even three don't run reliably once you start moving
the heads about.)

It would be interesting to compare RAIDframe with Disksuite, but I'm not
about to load Solaris just to test it....  Does anyone know of anyone
else running Disksuite on older drives on a Sparc-20 SM71?  ;-)

> If you really need 100mbps of nfs traffic, fairly consistently, you should
> be able to justify hardware raid.

I should hope so!  ;-)

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods at acm.org>      <robohack!woods>
Planix, Inc. <woods at planix.com>; Secrets of the Weird <woods at weird.com>