Saturday 11th August 2012 1.18pm

Sat, Aug 11, 2012

So, my 3Tb WD Red passed its 'badblocks' test which does four passes of write and read verification (only taking four days), so I passed it as a whole device into my Ubuntu #KVM running #zfsonlinux and configured it as a #ZFS pool device. I set it running copying all the files off my old NTFS external USB drive into the new ZFS pool and … well, it was taking a very, very long time. Turns out it was doing just 500Kb/sec, which even for KVM is abnormally slow.

So, I bump up RAM allocated to 4Gb, change it from direct device passthrough into a #LVM raw file (there used to be a slow write bug in KVM with direct device passthrough, but it's supposed to be fixed) and … still 500Kb/sec with dd from /dev/zero.

Ok I think, let's turn off all fsyncing and write barriers, so after passing 'cache=unsafe' for the LVM raw file into KVM, now I get … 1.2Mb/sec. Well, I suppose at least that's better :) but that's still a factor of 100x slower than it should be.

I guess it's time for the thinking cap to go on. There must be something I'm missing here!