Slow write to LVM with snapshot

Question

I use Ubuntu 10.04 Server. Write very slow, when I use LVM snaphot. This is normal?

Answer 1

This is normal?

Yes(Link1, Link2). On my server(4x SATA RAID):

# dd if=/dev/zero of=/data/test/foo count=10 bs=1024k
10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 0.103387 s, 97.3 MB/s

# dd if=/dev/zero of=/data/test2/bar count=10 bs=1024k
10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 0.722223 s, 13.8 MB/s

Answer 2

I experienced this, too. Using only SATA drives with diffrent combinations: with/without RAID 1/5/10 sw and hw. This is caused by high I/O usage by snapshot volume. I'm going to save snapshots on separate volumes... or use SAS/SCSI. usual SATA drive - around 300 tps usual SCSI drive - can do around 1000 tps and more Check by iostat what is going on in Your system.