Date: Sat, 13 Jul 1996 16:08:45 -0500 (CDT) From: Joe Greco <jgreco@brasil.moneng.mei.com> To: michaelv@HeadCandy.com (Michael L. VanLoon -- HeadCandy.com) Cc: pst@shockwave.com, hackers@freebsd.org Subject: Re: using ccd for striping? Message-ID: <199607132108.QAA00481@brasil.moneng.mei.com> 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
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