LVM resize sanity check

[Robert Locke]

On Wed, 2008-10-22 at 14:48 -0400, brian wrote:
> brian wrote:
> > Robert Locke wrote:
> >>
> >> As an alternative, that might be easier, why not install 
> >> "system-config-lvm"?  It presents a graphical view of shrinking and 
> >> enlarging.....
> > 
> > Thanks, I'll check that out.
> > 
> > 
> 
> That looks easy to use. However, I can't unmount /tmp so it looks like 
> I'll have to use a rescue CD and go with cmd line.
> 

Unmounting should only be necessary when "shrinking" a filesystem.  I
thought you were growing /tmp....  But, now that you mention it, I
didn't notice that you were unmounting and fscking /var before lvextend
and resize2fs.

Generally growing should work with just lvextend and resize2fs, because
you are only tacking things on to the end of the filesystem, not
touching most of the existing data structures.

Shrinking is the more interesting challenge, because you are looking at
the potential of "moving" data.  While this is handled just fine by
resize2fs, it is "strongly" recommended to e2fsck beforehand to ensure
you are starting from "stable structures".  So shrinking is normally:
umount, e2fsck, resize2fs, lvreduce, and mount.  The danger is that
lvreduce has no knowledge of the filesystem which resides on top of it,
so is perfectly happy with shrinking into "live" structures.  That's why
I was concerned with you using an "absolute" number for resize2fs and a
relative number for lvreduce earlier.  To easy to slip up and lvreduce
into the filesystem.

Good luck,

--Rob