How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs

Wed Aug 4 04:21:22 CDT 2010

On Wed, Aug 04, 2010 at 11:13:17AM +0200, Dominik Brodowski wrote:
> > show these problems?
> 
> No, 2.6.31 to 2.6.34 show similar behaviour.

Ok, so it's been around for a while.  Can you test the write speed of
each individual device layer by doing a large read from it, using:

	dd if=<device> of=/dev/null bs=8k iflag=direct

where device starts with the /dev/sda* device, and goes up to the MD
device, the dm-crypt device and the LV.  And yes, it's safe to read
from the device while it's otherwise mounted/used.