I came across a comment in this question which states that LVM over RAID or RAID over LVM is evil, and many people have up-voted the comment, so there must be some truth to it (I guess)!
However, I would like to know what exactly is so evil about LVM over RAID?
This is important because I actually need to setup a backup server and the only way to get a file system snapshot in XFS is via LVM.
I think there is some confusion and you misunderstood the comment. It just states that you should LVM on RAID but the other way around (and only that) in form of RAID on LVM is bad. These are two sentences, not one.
Read is at Use LVM on RAID. RAID on LVM is the devils work.
Why is this so bad? Simple: If you do this, your layout looks like this:
| / | /var | /usr | /home |
--------------------------
| RAID Volume |
--------------------------
| LV 1 | LV 2 | LV 3 |
--------------------------
| Disk 1 | Disk 2 | Disk 3 |
and you have created another level of indirection, increasing complexity and reducing performance and flexibility. In short, you will have gained not a single advantage but instead lost a lot of options.
The accepted answer also clearly states that using LVM on top of a RAID is perfectly fine (on spinning rust).
If you are after snapshots, look into using ZFS (or btrfs). ZFS can be a single stop replacement for RAID, LVM and XFS.
