Hi, Do you have suggestions on how to properly access SSD disks? Currently I have a RAID0 on two SSD disks, accessible as /dev/md0. md0 is used as a PV with LVM, on which I have a VG and a LV. The LV is seen as xvda by the VM. I am using the whole LV as a root device for the VM (no partitions). I am seeing up to 25% less performance on the VM when doing IO tests (not sure if I am doing the correct way to test IO). Do you have any suggestions if I can do this configuration better. Thanks. Lloyd IO tests with hdparm: Avg. cached reads xvda: 2586.68 MB/s Avg. cached reads md0: 2654.68 MB/s Difference (cached reads) entre xvda et md0: 97% -> 3% moins rapide sur VM --- Avg. buffered reads xvda: 357.67 MB/s Avg. buffered reads md0: 419.67 MB/s Difference (buffered read) entre xvda et md0: 85% -> 15% moins rapide sur VM IO tests with dd: vm:~ # time dd if=/dev/zero of=/var/tmp/zero.txt bs=1k count=10485760 10485760+0 records in 10485760+0 records out 10737418240 bytes (11 GB) copied, 118.399 s, 90.7 MB/s xen:/mnt/ioaccel_vm/var/tmp # time dd if=/dev/zero of=./zero-phy.txt bs=1k count=10485760 10485760+0 records in 10485760+0 records out 10737418240 bytes (11 GB) copied, 90.4089 s, 119 MB/s
On Mon, Sep 3, 2012 at 2:54 PM, Lloyd Dizon <thecarrionkind@gmail.com> wrote:> Hi, > Do you have suggestions on how to properly access SSD disks? > Currently I have a RAID0 on two SSD disks, accessible as /dev/md0. > md0 is used as a PV with LVM, on which I have a VG and a LV. > The LV is seen as xvda by the VM. I am using the whole LV as a root > device for the VM (no partitions).That works. Although if it''s raid0 I''d just use LVM directly without md. Or, since you seem to only use the SSD for the domU anyway, you can pass the SSDs (/dev/sd*) to domU, and do LVM there.> > I am seeing up to 25% less performance on the VM when doing IO tests > (not sure if I am doing the correct way to test IO).Nope :) Your test is basically influenced by cache. IMHO something like bonnie++ or fio (configured with random r/w) is better. And make sure your test size is at least twice the RAM. And there ARE some performance penalty in domU, though I don''t know what the "normal" number is nowadays. -- Fajar