[dm-devel] Re: DM performance issues

[Elliot Lee]

Sorry, I really should have given details on my system, especially  
the kernel version:

Linux 2.6.19-1.2911.fc6 #1 SMP x86_64

Pentium 4 3.00 GHz CPU, 1G RAM
ext3 on LVM on RAID-5 on 5 * 500G SATA drives.

Best,
-- Elliot

On Mar 7, 2007, at 19:36 , Elliot Lee wrote:

> 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
>