I have received a HP server with Ubuntu installed by someone else. There is Smart Array RAID controller installed there with cciss driver. And at the same time, there's device mapper configured:
$ ls -l /dev/mapper/ total 0 crw-rw---- 1 root root 10, 59 2010-08-25 19:01 control brw-rw---- 1 root disk 251, 0 2010-08-25 19:01 okd-root brw-rw---- 1 root disk 251, 1 2010-08-25 19:01 okd-swap_1 $ ls -l /dev/cciss/ total 0 brw-rw---- 1 root disk 104, 0 2010-08-25 19:01 c0d0 brw-rw---- 1 root disk 104, 1 2010-08-25 19:01 c0d0p1 brw-rw---- 1 root disk 104, 2 2010-08-25 19:01 c0d0p2 brw-rw---- 1 root disk 104, 5 2010-08-25 19:01 c0d0p5 $ mount /dev/mapper/okd-root on / type ext4 (rw,errors=remount-ro) ... /dev/cciss/c0d0p1 on /boot type ext2 (rw)
What I'm certain about is that hardware RAID is a must on my servers. Its battery-backed cache can provide a higher performance than that of software-only RAID. But should I get rid of the device mapper and LVM based on it?
From what I found in various sources, I thought I would better leave it as it is.
Firstly, the performance penalty is negligible. Secondly, LVM allows for more flexible volume management (like, removal of a PV, moving PEs to the free space in the VG). Thirdly, snapshots. And, finally, portability of LVM volumes between incompatible hardware (this won't work for me, I'm afraid, because of the underlying hardware RAID1).
Besides, this LVM over RAID approach seems to be a common thing now and nobody seems to have complained about it... :)
Well, anyway, I understood that Linux software RAID is one more area I should learn more about.
