Very slow migration of sites with data > 3 GB? High IO wait resulting in high load and unavailability.

Hi Guys We are starting to use Aegir on more and more customer sites, and have been experiencing some problems lately.

We have some sites with 3-4 GBs data on rather powerful virtual servers. When we migrate them to a new version of a platform it takes a really long time (20-50 mins), and during that migration the load on the server gets very high (due to IOWait as far as I can see), and the site gets unresponsive in the meantime (due to high serverload). One of the servers are specced with 8 CPUs, 16 GB ram and 100 GB SAN disk, running debian squeeze. The other is smaller specced but similar, and running Ubuntu.

When running IOtop while this is in process, I can see that Aegir runs a "gzip" command most of the time. When that task is finished, then the rest of the migration finishes very quickly.

Is this normal? Because even though SAN disks can be slow-ish, this seems excessive?

Thanks, Rasmus reload.dk