Improve export domain performance

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I will have to split a data center into two ones. Thus I will have to export/import large amount of VMs (about 3 TB in total). Could you please share your suggestions how to get the best performance in this process (tune nfs, any hints on RHEV side)?





Maybe you can try few options available on a single vm and see what works better for you.
The options you have, if your vms has snapshots:
- Delete snapshots before exporting and then export.
- Collapse snapshots while exporting.
- Do not collapse snapshots while exporting.

Maybe write a script that will copy the VMs one after another at night time, when there is less traffic and load?

I hope this helps.


We've undertaken many VM migration from both legacy KVM based RHEL clusters (using virt-v2v) and from RHEV to RHEV.
A few pointers from our experiences :-

  • Try and keep the NFS server that serves as your Export storage domain on the same network segments as your hypervisors. This prevents traffic traversing gateways. (I am told by RH support that it is best to define a separate logical network for the subnet of you NFS server if not on the same segments as your hypervisors to create a static route and prevent traffic over the default gateway. I'm yet to try this though)
  • Before carrying out an Export/Import, it is best that the the SPM node is clear of VM load. Since the SPM node carries out much of the Export/Import I/O, this should ensure that maximum bandwidth is available for the data migration and will not be hindered by any other management type activity or live-migrations (if you do not have a separate live-migration network). The high rate of I/O during an Export/Import operation has been know to block heartbeats and cause hypervisors to fence, but I think this is less of an issue with later versions of RHEV.

  • If you are carrying out many VM migrations, group similar sized (in terms of disk size) VMs together to Export/Import and consider using two Export storage domains ; one to Import whilst the other for Export and flip them back and forth. There nothing worse than waiting for one huge VM to complete Export then you could have been Importing 10 or so smaller ones that complete long before.

  • A VMs HA configuration is lost upon Export (pre 3.4). Ensure to correct this upon Import.