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List:       inet-access
Subject:    Re: SCSI RAID box to use for NFS Server
From:       Jason Philbrook <jp () saucer ! midcoast ! com>
Date:       2004-01-07 21:43:28
Message-ID: 20040107214328.GA29512 () saucer ! midcoast ! com
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On Wed, Jan 07, 2004 at 03:39:54PM -0500, John Capo wrote:
> Quoting Brian Feeny (signal@shreve.net):
> > On Jan 7, 2004, at 11:54 AM, Robert A. Hayden wrote:
> > >SCSI Raid has the same slowness during rebuild.  I use lots of 3wares 
> > >at
> > >home and at work and love 'em.
> > I understand there is going to be slowness.  But I am talking about so 
> > slow, that the system
> > load goes thru the roof, and the system becomes totally unusable.  In 
> > other words, the mail
> > server is no longer able to function.
> Some controllers allow you to set the rebuild rate so there is some
> disk and controller bandwidth left for real work.  If you lose a
> drive in a raid 5 partition its already costing you performance due
> to the raid system having to synthesize some of the data.  Toss in
> a rebuild on a busy machine and things get worse.

With Promise's rm series external raid boxes, you can set the rebuild 
process to either low or high priority. They use ATA100 drives and provide 
ultrascsi-160 to the computer.

Low priority rebuild takes about two days on a real busy system (so it
wouldn't affect performance much).  (whereas it would only be less tha two
hours on a new 120GB drive with no load) I haven't really timed it because 
it's at our datacenter, where I don't spend unnecessary time. We keep it 
full of disks. More disks = better performance.

Brian, if you are that close to load getting out of control, it sounds
like the I/O capacity is realy at the limit and has no room for any more
customers or changes in mail usage patterns. Probably backups as well as
other disk intensive things such as period mail queue flushes cause load
spikes too. At that point, it's time to either upgrade to bigger hardware
or distribute the load. (Choose the second option)

-- 
/*
Jason Philbrook   |   Midcoast Internet Solutions - Internet Access,
    KB1IOJ        |  Hosting, and TCP-IP Networks for Midcoast Maine
 http://f64.nu/   |             http://www.midcoast.com/
*/
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