RAID 5 in software is notoriously horrible, which probably explains the crappy write rates you experienced. It would be interesting to know what the read rates were - I'd expect them to be much better.
An alternative would be to configure the device as RAID 1 (or 10, 0+1 whichever it supports). This should have far better performance, and ought to give you the same storage as 5 + hot spare (two disks worth in each case). Of course, you've lost the hot spare in that case, which might be an issue.
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RAID performance
RAID 5 in software is notoriously horrible, which probably explains the crappy write rates you experienced. It would be interesting to know what the read rates were - I'd expect them to be much better.
An alternative would be to configure the device as RAID 1 (or 10, 0+1 whichever it supports). This should have far better performance, and ought to give you the same storage as 5 + hot spare (two disks worth in each case). Of course, you've lost the hot spare in that case, which might be an issue.
-- Tim