Date: Mon, 10 Dec 2001 10:49:28 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Wilko Bulte <wkb@freebie.xs4all.nl> Cc: Mike Smith <msmith@FreeBSD.ORG>, Terry Lambert <tlambert2@mindspring.com>, Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de>, freebsd-current@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern subr_diskmbr.c Message-ID: <200112101849.fBAInSO47847@apollo.backplane.com> References: <200112101754.fBAHsRV01202@mass.dis.org> <200112101813.fBAIDKo47460@apollo.backplane.com> <20011210192251.A65380@freebie.xs4all.nl>
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:For RAID3 that is true. For the other ones...
:
:> performance without it - for reading OR writing. It doesn't matter
:> so much for RAID{1,10}, but it matters a whole lot for something like
:> RAID-5 where the difference between a spindle-synced read or write
:> and a non-spindle-synched read or write can be upwards of 35%.
:
:If you have RAID5 with I/O sizes that result in full-stripe operations.
:
:--
:| / o / /_ _ email: wilko@FreeBSD.org
:|/|/ / / /( (_) Bulte Arnhem, The Netherlands
Well, for reads a non-stripe-crossing op would still work reasonably
well. But for writes less then full-stripe operations without
spindle sync are going to be terrible due to the read-before-write
requirement (to calculate parity). The disk cache is useless in that
case.
-Matt
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