[CentOS] pvmove speed

[William L. Maltby]

On Tue, 2008-02-12 at 20:41 -0700, Joseph L. Casale wrote:
> >You could "nice" it. "man nice". Since there is likely to be a lot of
> >I/O happening, it may not help much.
> 
> Ok, here's a noob question :) - What process would I nice?

If you run pvmove from the command line, "nice -20 pvmove" for example.
If you start lvm and run pvmove inside that, then "nice -20 lvm" e.g.

But based on the  1% CPU usage, probably won't help much.

> 
> >If the drives are on the same channel, or other devices on the channel
> >are also flooding the channel, that would be expected. Does "swapon -s"
> >show a lot of swap being used? Does top give a clue? I suspect a lot of
> >CPU may also be involved.
> 
> Swapon -s shows 0 being used, top shows cpu's next under 1%.

My guess then is that the writes to the HD are just large and slow. If
the two HDs on the same channel that would make it even slower. If the
drives are older/slower models, ditto. If they have small on-board
cache, same thing.

But I really have a hunch that it is just a lot of I/O wait time due to
either metadata maintenance and checkpointing and/or I/O failures, which
have very long timeouts before failure is recognized and *then*
alternate block assignment and mapping is done.

> 
> Thanks!
> jlc
> <snip sig stuff>

-- 
Bill