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From: Joe Greco <jgreco@brasil.moneng.mei.com>
Message-Id: <199607132108.QAA00481@brasil.moneng.mei.com>
Subject: Re: using ccd for striping?
To: michaelv@HeadCandy.com (Michael L. VanLoon -- HeadCandy.com)
Date: Sat, 13 Jul 1996 16:08:45 -0500 (CDT)
Cc: pst@shockwave.com, hackers@freebsd.org
In-Reply-To: <199607132058.NAA06514@MindBender.HeadCandy.com> from "Michael L. VanLoon -- HeadCandy.com" at Jul 13, 96 01:58:43 pm
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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.)

[...]

> 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.

Think about the case where you are not optimizing for bandwidth, but for
transactions per second.  Think "news spool"  :-)

Now think about the size of a cylinder group.

;-)  Not all problems get solved the same way.  I'd rather have a disk with
no improvement in bandwidth but a definite improvement in terms of how fast
an average random access is.  If you have two heads, and 'zones' on the
disk..

... JG