Areca vs. ZFS performance testing.
Dieter
freebsd at sopwith.solgatos.com
Wed Nov 12 23:30:30 PST 2008
>> 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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