I'm having performance issues using a zpool consisting of 4 2TB Seagate LP disks on FreeNAS 8.0.2. I have followed the testing recommendations in this thread most of the time -- though admittedly not with every variation, as it's time-consuming. I'm running an HP Proliant Microserver with 5GB of RAM.
My performance is fine (write ~191MB/s, which seems far too high to me, but anyway) when using a zpool consisting of three disks or fewer. As soon as I create one with four disks, however, the performance degrades enormously: I end up with write speeds of about 6MB/s (though I couldn't write as much as 100GB with that, as it would have taken too long).
Using iostat, I've been able to determine that one of the four disks constantly performs slower than the others, maintaining speeds of around 6500kB/s, while the others generally hover around 100,000kB/s. The other disks cease to write at all for long periods of time, as they seem to wait for the slow disk to catch up. There does not appear to be a problem with the disk: the slow-performing disk seems to vary each time a 4-disk pool is created, and all four disks seem to work fine when I create two separate zpools, each containing two disks.
I've tried 4-disk configurations with and without the 4k setting (I believe these are 4k disks), and with all combinations of stripe, mirror, raidz1 and raidz2. (My preference is for raidz1.) The result is the same.
I have also tried a 4-disk striped configuration in UFS. In that situation, I receive considerably slower write speeds (~25MB/s), but the performance is the same for all four disks.
Does anybody have any advice for me? I know I'm running with only 1GB above the minimum memory requirement -- could that be the problem?
My performance is fine (write ~191MB/s, which seems far too high to me, but anyway) when using a zpool consisting of three disks or fewer. As soon as I create one with four disks, however, the performance degrades enormously: I end up with write speeds of about 6MB/s (though I couldn't write as much as 100GB with that, as it would have taken too long).
Using iostat, I've been able to determine that one of the four disks constantly performs slower than the others, maintaining speeds of around 6500kB/s, while the others generally hover around 100,000kB/s. The other disks cease to write at all for long periods of time, as they seem to wait for the slow disk to catch up. There does not appear to be a problem with the disk: the slow-performing disk seems to vary each time a 4-disk pool is created, and all four disks seem to work fine when I create two separate zpools, each containing two disks.
I've tried 4-disk configurations with and without the 4k setting (I believe these are 4k disks), and with all combinations of stripe, mirror, raidz1 and raidz2. (My preference is for raidz1.) The result is the same.
I have also tried a 4-disk striped configuration in UFS. In that situation, I receive considerably slower write speeds (~25MB/s), but the performance is the same for all four disks.
Does anybody have any advice for me? I know I'm running with only 1GB above the minimum memory requirement -- could that be the problem?
