Date: Thu, 30 Nov 2006 11:57:03 -0800 From: Chuck Swiger <cswiger@mac.com> To: Derrick MacPherson <dmacpher@vfs.com> Cc: freebsd-questions@freebsd.org Subject: Re: degraded RAID performance after OS upgrade, and drives added. Message-ID: <F1D1E8AF-FEDD-440C-B2ED-3601F2407ABD@mac.com> In-Reply-To: <200611301942.kAUJgMiv012412@mac.com> References: <200611301942.kAUJgMiv012412@mac.com>
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On Nov 30, 2006, at 11:40 AM, Derrick MacPherson wrote: > That seems like a pretty crazy drop in performance, more than one > would expect. The machine is busy but not busy enough to warrant > this.. Imo.. Is there a way to test to confirm? Using dd is a trivial benchmark, and not especially precise but good enough to give rough answers; otherwise, there are lots of I/O benchmarks in ports like iozone or even "diskinfo -t". Try using different block sizes while reading and writing with dd, and you'll probably find some useful info. While it is likely that you can adjust the RAID-5 stripe size, change the write-caching from write-thru to write-back (if your RAID has a battery, anyway, otherwise this is dangerous), etc, using a 3-disk RAID-5 volume is just not a great idea-- RAID-5 is happier with more drives than the minimum of 3 to get better parallelism and reduce the overhead for parity info. -- -Chuck
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