Question about reprotecting VM and data that gets replicated back

[dwalwyn]

Hello,

After completing a failover of, say, a 40GB virtual machine from site A to site B, if we choose to click on the reprotect button to reverse the replication back from site B to A, does SRM replicate the full 40GB VMDK of the virtual machine from Site B back to Site A or is there some sort of method that SRM maintains deltas so that we don't have to replicate the full virtual machine back?

This will help us with planning how long it would take to failback our infrastructure if we choose to failover to another site.

Thank you.

[Mattallford]

Is this using vSphere replication, array based replication or something else?

With vSphere Rep / ABR, a full re-sync of the data from site B to A should not be required.

Cheers, Matt.

[dwalwyn]

This is using vSphere replication.

Great.  The status we see:

Status: Initial Full Sync

... is a bit confusing because it seems to imply that the whole virtual machine is being copied over back to site A again but the time it takes to complete seem to be a lot faster than what it should have taken to copy a full 40GB over to our site A from site B.

Would you be able to let me me know what data it is resynching then?  The documentation isn't too clear on that. Thanks.

Site Recovery Manager 5.5 Documentation Center

vSphere Replication Synchronization Types - VMware vSphere Blog

VMware vCenter Site Recovery Manager 5.8 Documentation Center

[Mattallford]

Hrmm, how about this:

If data is similar on each of the storage devices (that is, the original copy has already been made), but now the two sides are out of sync, is a new copy made, or are changes sent?

If no changes to the disk have been made "behind the back" of the vSphere Replication infrastructure, then only deltas (sets of changed blocks) are sent to complete a new copy.

If the disks are changed out of purview of the vSphere Replication infrastructure (or if the virtual machine is new to vSphere Replication), the vSphere Replication system compares the disks (without sending the content, just checksums between sites) to re-establish its state, then sends deltas going forward. This complete disk synchronization step involves reading the entire disk at each site, but matching disk blocks are not re-sent.

From https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=20057...

[admin]

Just to add to Matt's reply, this is covered in the Reprotect documentation:

"When performing reprotect with vSphere Replication, Site Recovery Manager uses the original VMDK files as initial copies during synchronization. The full synchronization that appears in the recovery steps mostly performs checksums, and only a small amount of data is transferred through the network."

Site Recovery Manager 5.5 Documentation Center

I agree the "initial full sync" that appears in the UI can cause confusion.

[dwalwyn]

Thanks everyone!