Date: Tue, 11 Dec 2001 11:06:33 +1030 From: Greg Lehey <grog@FreeBSD.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Wilko Bulte <wkb@freebie.xs4all.nl>, Mike Smith <msmith@FreeBSD.ORG>, Terry Lambert <tlambert2@mindspring.com>, Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de>, freebsd-current@FreeBSD.ORG Subject: RAID performance (was: cvs commit: src/sys/kern subr_diskmbr.c) Message-ID: <20011211110633.M63585@monorchid.lemis.com> In-Reply-To: <200112101830.fBAIU4w47648@apollo.backplane.com> References: <200112101754.fBAHsRV01202@mass.dis.org> <200112101813.fBAIDKo47460@apollo.backplane.com> <20011210192251.A65380@freebie.xs4all.nl> <200112101830.fBAIU4w47648@apollo.backplane.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Monday, 10 December 2001 at 10:30:04 -0800, Matthew Dillon wrote:
>
>>> 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.
>
> Well, 'more then one disk' operations anyway, for random-I/O. Caching
> takes care of sequential I/O reasonably well but random-I/O goes down
> the drain for writes if you aren't spindle synced, no matter what
> the stripe size,
Can you explain this? I don't see it. In FreeBSD, just about all I/O
goes to buffer cache.
> and will go down the drain for reads if you cross a stripe -
> something that is quite common I think.
I think this is what Mike was referring to when talking about parity
calculation. In any case, going across a stripe boundary is not a
good idea, though of course it can't be avoided. That's one of the
arguments for large stripes.
Greg
--
See complete headers for address and phone numbers
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20011211110633.M63585>