On an internal mailing list we had a very useful discussion around storage migrations when a SAN is replaced or a migration needs to take place to a different set of disks. Many customers face this at some point. The question usually is what is the best approach? SAN Replication or Storage vMotion… Both have its pros and cons I guess.
- Can utilize Array based copy mechanisms for fast replication (+)
- Per LUN migration, high level of concurrency (+)
- Old volumes still available (+)
- Need to resignature or mount the volume again (-)
- A resignature also means you will need to reregister the VM! (-)
- Downtime for the VM during the cut over (-)
- No downtime for your VMs (+)
- Fast Storage vMotion when your Array supports VAAI (+)
- If your Array doesn’t support VAAI migrations can be slow (-)
- Induced cost if VAAI isn’t supported (-)
- Only intra Array not across arrays (-)
- No resignaturing or re-registering needed (+)
- Per VM migration (-)
- Limited concurrency (2 per host, 8 per vmfs volume) (-)
As you can see both have its pros and cons and it boils down to the following questions:
How much down time can you afford?
How much time do you have for the migration?