Linux – this dm-0 device

linuxubuntu-9.10

While poking around trying to figure out why a Linux -> Linux file transfer is running slower than I think it should, I stumbled across something I'm not familiar with. /dev/dm-0 seems to be my bottleneck, but I have no idea what it is.

On my destination server, the iostat command shows a device at the bottom, /dev/dm-0, as being 100% utilized. This server has 6 disks in a mdadm raid5 set, with LVM running on top of it. Each of the underlying disks are sitting around 50% util. The transfer is writing to a logical volume located on this raidset.

What is this /dev/dm-0 thing? Once I know what it is, maybe I can find how to increase its speed, or at least understand why its the speed that it is.

It's part of the device mapper in the kernel, used by LVM. Use dmsetup ls to see what is behind it.