Date: Sat, 13 Jul 1996 13:58:43 -0700 From: "Michael L. VanLoon -- HeadCandy.com" <michaelv@HeadCandy.com> To: Joe Greco <jgreco@brasil.moneng.mei.com> Cc: pst@shockwave.com (Paul Traina), hackers@freebsd.org Subject: Re: using ccd for striping? Message-ID: <199607132058.NAA06514@MindBender.HeadCandy.com> In-Reply-To: Your message of Sat, 13 Jul 96 14:27:54 -0500. <199607131927.OAA00314@brasil.moneng.mei.com>
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>> Is anyone using the ccd driver in striping mode? I'd like to hear about
>> other people's good/bad experiences before trying it out myself.
>
>I've seen it act a little funny with way large stripe sizes (65536), several
>different times I have seen it develop "non-writable" and "non-accessible"
>zones near the very end of the disk.
I presume you're talking about the interleave factor? Since you say
large, and 65536, I assume you're saying 64MB stripes? (64K disk
blocks, 32K bytes, wouldn't be "large".)
Is there a good reason for doing that? I would think you'd get a much
better performance boost by going with interleaved stripes somewhere
between the size of a filesystem cluster to a unit the size of the
smallest drive's cache. (When I say "cluster", I am referring to the
size of a filesystem block -- 8 fragments -- not a disk block -- 512
bytes.)
I have been going with a 128 block (64K) interleave, since that's half
the size of my drives' caches, and is the size of four filesystem
clusters (whichh I have allocated as 16K).
Any bigger than that and you lose all the benefits of interleaved
access. In fact, I have considered reducing it to 16K so it would
interleave on single-cluster sizes.
On the other hand, if you get too fine of an interleave, you can get
inefficient since the ccd driver will be doing a lot of work reading
in lots of small pieces and assembling them.
Still, I can't think of any reason you'd ever want 64MB interleaved
stripes. I don't see any benefit in such an arrangement.
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Michael L. VanLoon michaelv@HeadCandy.com
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