I have a long-term goal of setting up a DR site in a colo somewhere and part of that plan includes replicating some volumes of my EqualLogic SAN. I'm having a bit of a difficult time doing this because I don't know if my method is sound.
This post may be a bit lengthy for the sake of completeness.
Generally relevant information:
- I have one EqualLogic PS4000X (~4TB).
- The SAN Acts as shared storage for 2 ESXi hosts in vSphere 5 environment.
- I have 4 volumes of 500GB each. Volumes 1 and 2 contain my "tier 1" VMs. These will be the only volumes I plan to replicate.
- Currently have 3Mb/s connection with actual data bandwidth at ~2.8Mb/s because of our PRI(voice).
My method of measuring change in a volume:
I was told by a Dell rep that a way (perhaps not the best?) to estimate deltas in a volume is to measure the snapshot reserve space used over a period of time of a regular snapshot schedule.
My first experiment with this was to create a schedule of 15 minutes between snapshots with a snapshot reserve of 500GB. I let this run overnight and until COB the following day. I don't recall the number of snapshots that could be held in 500GB but I ended up with an average of ~15GB per snapshot.
$average_snapshot_delta = $snapshot_reserve_used / $number_of_snapshots
I then changed the snapshot interval to 60 minutes which after a full 24 hours passing means a total of 13 snapshots in 500GB. This leaves me with ~37GB per hour (or ~9GB per 15 mins).
These numbers are astronomical to me. With my bandwidth I can do a little over 1GB/hour with 100% utilization. Is block-level replication this expensive or am I doing something completely wrong?