[linux-lvm] performance probs: snapshots on mp-systems

[Martin Petermann]

Hi all,

I have running SuSE 7.2 (2.4.4 kernel) on a dual processor machine (2x833
Mhz Pentium III). I made a snapshot of the following configuration:

>lvcreate -L 100M -n snapshot -c 4 -s /dev/vgfortest/testfs1
lvcreate -- WARNING: the snapshot will be automatically disabled once it
gets full
lvcreate -- doing automatic backup of "vgfortest"
lvcreate -- logical volume "/dev/vgfortest/snapshot" successfully created

peanuts:root /
>lvscan
lvscan -- ACTIVE            "/dev/mediastore/data" [100 GB]
lvscan -- ACTIVE            "/dev/vgfortest/bigfs" [8 GB]
lvscan -- ACTIVE   Original "/dev/vgfortest/testfs1" [500 MB]
lvscan -- ACTIVE            "/dev/vgfortest/testfs3" [500 MB]
lvscan -- ACTIVE            "/dev/vgfortest/smallfs" [60 MB]
lvscan -- ACTIVE   Snapshot "/dev/vgfortest/snapshot" [98.54 MB] of
/dev/vgfortest/testfs1
lvscan -- ACTIVE            "/dev/zweite_testvg/testfs1" [500 MB]
lvscan -- ACTIVE            "/dev/zweite_testvg/testfs3" [500 MB]
lvscan -- ACTIVE            "/dev/zweite_testvg/testfs" [200 MB]
lvscan -- 9 logical volumes with 110.3 GB total in 3 volume groups
lvscan -- 9 active logical volumes

The vg vgfortest is on a fc disk.

This first run I did in multi processor mode:

>time cat /dev/vgfortest/snapshot > /BIGFS/file
 1136.72s real     0.13s user    15.87s system

in single processor mode:

peanuts[root]/> time cat /dev/vgfortest/snapshot > /BIGFS/file
  402.03s real     0.10s user    16.16s system

Is this problem known? Does there exist a fix?

Thanks for any help!

Martin