[linux-lvm] pvmove speed

Roy Sigurd Karlsbakk roy at karlsbakk.net
Fri Feb 17 17:33:31 UTC 2017

> Roy> I get 200MB on a cold day and 500 on a nice one from this
> Roy> SAN. These 40-50MB/s seem really being limited by pvmove
> Roy> alone. Nothing else shows this limit. That's why I'm asking.
> Roy> Vennlig hilsen / Best regards
> Is any one CPU pegged on your server running the pmove?  It's probably
> single threaded and if it's a single LV you're moving, that might
> explain the problem.

No. CPU is hardly in use at all, and the little is spread across all four vcores - https://karlsbakk.net/tmp/pvmove-top.png. It's running on a very low-traffic host.

> It might also be that even though you have 4 x 1gb to one server,
> since it's the same IP pair on each end, it's not really spreading the
> load across all the links.

That would make sense if I got around 100MB/s from that, but I get a *total* of 100MB/s, read and write inclusive. The host machine is connected to 10Gbps, the new storage, dell compellent, is on 10Gbps, everything, really is 10Gbps except the old equallogic stuff, being on 4x1Gbps. For utilisation and bandwidth, see the munin graphs here https://karlsbakk.net/tmp/pvmove-munin.png. A pvmove /dev/sdc /dev/sde is currently running

> It might be faster to do a clone on the source side, and then use DD
> to copy the data from the quiet clone to the destination.  Then mount
> the destination and use rsync to bring them up to sync.

It's not practically possible, since the amount of data is too high. Thus pvmove, to allow for concurrent use.

> But it would be helpful to see more details about the OS, etc.

It's not much to say - standard RHEL7 with some bits from EPEL, but basically just the normal bits. System is running on an ESXi 6.5 host. Old storage is raw device mappings to an Equallogic box (or two), new storage is VMFS 6. I really can't see any issues here, except the fact that the utilisation of sdc + sde == 100 and that this is constant.

So - any ideas?

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