[lug] Server Partitioning Recommendation

[Daniel Webb]

On Thu, Jan 18, 2007 at 06:44:03PM -0700, dio2002 at indra.com wrote:

> I thought the whole purpose of LVM was so that you "can" span multiple
> physical devices.  Why would I not want to span LVM across physical
> devices?

There was a discussion on this subject a while back on this list where I
played devil's advocate.  Basically, you divide your mean time before failure
by the number of drives if you span multiple physical devices with a logical
volume.  I can't remember my statistics class well enough, but it's probably
not that simple.  I'll pretend though.  ;)

One of the things I got from that conversation, though, is that anybody who
spans devices with LVM better be spanning RAID devices or at least understand
the risk they're taking (it could be OK if you have very solid automated
backups, for instance).

I'm curious, though, what happens when you put LVM on RAID5 and then add a
drive to it?