On Sat, May 17, 2008 at 11:11:51AM +0200, Hans-Joachim Baader wrote: > Hi, > > 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. Strange config, good result ;) > > 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 2.6.23.12 and 2.6.25.1 on AMD64 X2. > Is it possible to get 210 MB/s? Have you tried fiddling with read ahead ? "blockdev --setra ..." on the striped LV. > > Thanks, > hjb > -- > Pro-Linux - Germany's largest volunteer Linux support site > http://www.pro-linux.de/ Public Key ID 0x3DDBDDEA > _______________________________________________ > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ -- Regards, Heinz -- The LVM Guy -- *** Software bugs are stupid. Nevertheless it needs not so stupid people to solve them *** =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com PHONE +49 171 7803392 FAX +49 2626 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
