[linux-lvm] Performance of striping
hjb at pro-linux.de
Mon May 19 19:01:26 UTC 2008
> > But this setup was too complicated for me, so I tried a different
> > approach. Still a physical volume for each disk (actually partiton 2
> > which is nearly the complete disk), but only one volume group vg0.
> > The commands used were:
> > pvcreate /dev/sda2
> > pvcreate /dev/sdb2
> > pvcreate /dev/sdc2
> > vgcreate vg0 -s 128 /dev/sda2 /dev/sdb2 /dev/sdc2
> > On vg0, I created a LV which should span all 3 disks and therefore be
> > equivalent to a RAID 0:
> > lvcreate --name=test -L 10000M -i 3 vg0
> > Resulting LV:
> > --- Logical volume --- LV Name /dev/vg0/ubuntu VG Name vg0
> > LV Write Access read/write
> > LV Status available
> > # open 1
> > LV Size 10,12 GB
> > Current LE 81
> > Segments 1
> > Allocation inherit
> > Read ahead sectors 0
> > Block device 254:10
> > However, I get only half the expected performance. I created an XFS
> > filesystem and mounted it on /mnt/tmp:
> > # dd if=/dev/zero of=/mnt/tmp/bla bs=1024k count=10000
> > 10485760000 Bytes (10 GB) kopiert, 112,233 Sekunden, 93,4 MB/s
> > # dd if=/mnt/tmp/bla of=/dev/null bs=1024k count=10000
> > 10485760000 Bytes (10 GB) kopiert, 88,8886 Sekunden, 118 MB/s
> > This was measured with kernel 18.104.22.168 and 22.214.171.124 on AMD64 X2.
> > Is it possible to get 210 MB/s?
> Have you tried fiddling with read ahead ?
> "blockdev --setra ..." on the striped LV.
read ahead is currently 256 on all devices. Thanks for the hint.
I will try some other values. Any Idea what is recommended?
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