[mythtv] Problems with using LVM for large storage

[Aran Cox]

On Mon, May 16, 2005 at 12:29:56PM -0500, Robert Kulagowski wrote:
> >This is actually a straightforward procedure and can be done with your
> >system up and running. I recently had a disk in my LVM began to fail and
> >I needed get all of the data off of it. I connected another drive and
> >added it to the volume group (pvcreate followed by vgextend). Then I got
> >the LVM to move all of the data off of the bad drive (pvmove) and then
> >dropped that drive from my volume group (vgreduce). I was able to do all
> >of this with the filesystem live, mounted and in use.
> 
> The last time I needed to do something like this pvmove would only work 
> if the new drive that was added was the same size or larger than the one 
> failing.  So adding 2 80GB drives to rescue the data from one failing 
> 120GB drive didn't work.  Sure, I could have done fancy tricks like 
> RAID0'ing the 80GB drives then adding _that_, but the complexity would 
> have made things even harder to fix later on if there were issues.

LVM has been able to do what you describe for literally years.  How
long ago did you try this?  Probably, you would have had to execute
two pvmove commands, one moving the first chunk to one disk and
another for the remaining chunk.  LVM doesn't have a concept of drives
anyway, it's got physical volumes and physical extents.  You needed to
move some extents from one PV to another PV.  I think you just didn't
spend enough time with the LVM FAQ and pvmove man page ;)

Aran