[clug] a few LVM questions

[Daniel Pittman]

Andrew <andrew at donehue.net> writes:

> I'm running a few virtual machines on a LVM volume (and I have some space on
> the base partition for snapshots).
>
> I have been allocating 3GB for a snapshot (and then rsync the vm's to
> another server).  I was wondering if there is any way to work out how much
> of this space is actually being used?

In the snapshot?  Run lvs as root and it will show you the percentage of space
consumed; it probably supports other figures as well, but I never bothered to
look for them.  That one fact has been enough for me.

[...]

> I also noticed that when I create the snapshot it blocks all writing for the
> virtual machines when the snapshot is being created (which does create some
> problems from time to time),

Correct.  It necessarily blocks writes while it creates the snapshot
mappings.  That shouldn't take more than a second or two, though, and the
writes are stopped from hitting disk, not much more, generally.

> googling around said that this wasn't a problem in earlier kernels, but some
> other users have noticed this as well.  Anyhow, was wondering if anyone else
> had experienced this?

Nope.  Snapshots are as fast as they always were.

        Daniel

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