Date: Wed, 12 Nov 2008 22:57:58 +0000 From: Dieter <freebsd@sopwith.solgatos.com> To: freebsd-fs@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: Areca vs. ZFS performance testing. Message-ID: <200811130657.GAA26763@sopwith.solgatos.com> In-Reply-To: Your message of "Thu, 13 Nov 2008 15:46:32 %2B1000." <491BBF38.9010908@dannysplace.net>
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>> For the array(s) >> 9 x ST31000340AS 1tb disks >> 1 x ST31000333AS 1tb disk (trying to swap this for a ST31000340AS) > There seems to be little difference between enabling and disabling the > disk cache on the Areca. This leads me to two conclusions: > 1. Disabling the write cache does nothing on Seagate drives. > 2. IO to the drives is so slow that a write cache is irrelevant. I have a couple of the ST31000340AS 1TB disks as well as older lower capacity Seagates, and turning the write cache on/off makes a MASSIVE (roughly 10:1) difference in write speed. Jeremy reports "about 13%" with Seagate ST3120026AS: http://lists.freebsd.org/pipermail/freebsd-hardware/2008-October/005450.html Perhaps there is something about the Areca or the testing? Is the write cache really getting turned on/off? You're getting about 2-3x the speed I'd expect if the write cache were off, so maybe it is still on but there is a bottleneck elsewhere? Have you tried a simple test with /dev/zero and dd to a raw drive to eliminate the effects of the filesystem?
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