Date: Fri, 17 Mar 2000 10:18:03 -0800 From: Greg Lehey <grog@lemis.com> To: Michael Hughes <mhughes@logroad.bridge.com> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: vinum strip size Message-ID: <20000317101803.I604@mojave.worldwide.lemis.com> In-Reply-To: <200003171417.IAA14294@logroad.bridge.com>; from mhughes@logroad.bridge.com on Fri, Mar 17, 2000 at 08:17:10AM -0600 References: <200003171417.IAA14294@logroad.bridge.com>
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On Friday, 17 March 2000 at 8:17:10 -0600, Michael Hughes wrote:
> Is there an easy way to come up with the strip size to use when striping
> disks?
No.
A number of factors influence the stripe size:
1. You want a stripe large enough that any one I/O will normally fall
on a single disk. This maximizes the subsystem bandwidth (in
other words, it maximizes performance as seen from the total
throughput perspective).
2. You want a stripe size which will ensure even distribution of the
ufs superblocks across all subdisks of the plex.
Getting (1) is easy: make it at least 256 kB. Getting (2) depends on
the number of subdisks. I've written a program for it, but it's not
really ready for prime time yet. The important thing is to recognize
that cylinder groups are almost invariably 32 MB in size, so any power
of two stripe size will give you the worst case situation and put all
the superblocks on a single subdisk.
Greg
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