[dm-devel] DM performance issues

[Elliot Lee <sopwith gmail com>]

Hi all,

I've got a 1.8TB LVM-on-RAID filesystem that was performing OK but  
really didn't seem like it was going as fast as it should. I ran the  
commands below and got some pretty startling results...

A 60% performance hit for a linear mapping is heinous. What can I do  
to help get this fixed?

Best,
-- Elliot

# dmsetup create foo --table '0 3880910848 linear 9:0 0'

# dd if=/dev/md0 of=/dev/null bs=1048576 count=4096
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 20.2362 seconds, 212 MB/s

# dd if=/dev/mapper/foo of=/dev/null bs=1048576 count=4096
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 55.3597 seconds, 77.6 MB/s