[linux-lvm] Performance of striping
hjb at pro-linux.de
Sat May 17 09:11:51 UTC 2008
last year I built a server with 3 SATA disks. I used a physical volume
for each disk, a volume group on each, and then created identical LVs
in each VG. Then I used dmesetup to create a RAID 0 over all 3 disks.
A single disk has an I/O performance of 70 MB/s. After creating a
filesystem on the RAID and measuring its performance I got the expected
result: 210 MB/s.
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:
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
--- 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
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 220.127.116.11 and 18.104.22.168 on AMD64 X2.
Is it possible to get 210 MB/s?
Pro-Linux - Germany's largest volunteer Linux support site
http://www.pro-linux.de/ Public Key ID 0x3DDBDDEA
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