VM Replication Traffic

[aix0]

Hi Chaps

Replicating a data store which hosts VMs from a primary to a secondary SAN, I have noticed that the data size is significantly higher than what I had originally anticipated. In order to save on potentially wasteful replication traffic, I have already taken measures to move the VM swap file to separate, non-replicated volume - which rules out the VM swap file causing the issue. I'm now considering moving the OS page files to a separate, non-replicated volume also, as I believe that could be the cause of the overly-high rate of data change.

I have monitored the guest VMs' page file usage and have noticed that on the 3 Server 2003 Standard machines, there is a continual page file utilisation of approximately 15%. These 2003 machines have 4GB of RAM allocated and probably run at around 50% virtual memory utilisation - so, they're not being pushed to their limits. There are also 2 Server 2008 machines residing on the same host which share the same qualities, 4GB of RAM, 50% utilisation, but 0% page file utilisation. The 2003 machines are Terminal Servers, so I'm guessing that the cause for the page file usage is down to idle / disconnected sessions, whereas the 2008 machines provide file and print services, which don't tend to tie up resource for prolonged periods of time.

So, to cut to the chase - what are people's thoughts on this? Is offloading the OS page file usual practice in a replicated environment? Has anyone tried this configuration before? Is there anything that I'm missing? Maybe the page file isn't to blame?

Just to fill you in on some statistics, there's 5 VMs in total, as mentioned above. The replication traffic for the VM host volume varies between 1 - 2GB (per hour) depending on time of day. The hypervisor is ESXi 4.1 update 1, running on R710s with Equallogic SANs.

Any comments / suggestions appreciated!

Thanks

Martin

 

[aix0]

Thanks for replying.

Well, that's sorted then, I'll get that set up this weekend if I get the time.

I'm not using SRM yet, but planning to implement over the next 2 months. So any info that you've got on that would be appreciated.

Thanks

 

[aix0]

I moved the page file from each machine, but it has had little affect on the overall replication size.

I've been using perfmon and task manager to monitor disk I/O and it doesn't really add up. I don't see a high volume of writes on any of the disks - which has left me slightly confused.

Strangely, the replication data size was approximately 1 - 2GB previously, whilst the VMs were replicating every hour. I've now adjusted the schedule and configured the volume to replicate every 6 hours - which produces 2 - 3GB, not a significant increase, like I had expected.

Any suggestions, Chaps?

Thanks

 

[aix0]

I'm using the EqualLogic VMware snapshot management tools (ASM/VE) to do the replicaiton - it's effectively a Linux based VM that uses the SDK to do snapshots and the like.

I was running this VM on the same VM datastore that I'm replicating, but I'm certain that it wouldn't have any affect on the replication size. I have moved the management VMs over on to a separate datastore this morning, to see if it does actually have any impact - just for peace of mind.