VSAN Resync running

[fifthman_roshan]

Hi.. I have a questions here. Any help would be appreciate

VSAN cluster with 6 hosts. VSAN size is 124TB. I migrated all VM from 1 hosts to others and removed hosts from the VSAN cluster to update BIOS and firmware.

Brought back up online within 30 mins and added back to cluster. Moved some VM's on it. ALL good.

Now i need to move to next host, however i see that the resync is still running and it says 14 days left to resync.

Is it advisable to still go ahead and take out another host for BIOS upgrade.. ?

[TheBobkin · Accepted solution]

Hello fifthman_roshan​

"I migrated all VM from 1 hosts to others and removed hosts from the VSAN cluster to update BIOS and firmware."

Just so you are aware, migrating VMs off a vSAN host doesn't move the data that resides on the locally-attached storage on that host - that's what MM(Maintenance Mode) with FDM(Full Data Migration) is for (or EA(Ensure Accessibility) which basically just relies on the existing data-mirror while the host is in MM).

Removing the host from the cluster for updates is not necessary nor advised (especially without a MM)

"Brought back up online within 30 mins and added back to cluster."

With default clom repair delay timer (60 minutes) it won't start rebuilding data until a host has been in MM/offline for this time period (unless you click 'Repair Immediately' via the Health UI or RVC), but if you remove the host from the cluster (and depending how) it may have started repairing data back to FTT=1.

"Now i need to move to next host, however i see that the resync is still running and it says 14 days left to resync.

Is it advisable to still go ahead and take out another host for BIOS upgrade.. ?"

No, wait until resync has completed and use MM rather than removing host from cluster - use EA or FDM mode, your choice but understand that FDM takes longer as it has to move all data off, but EA essentially makes FFT=1 data FTT=0 until the host is back, out of MM and the delta data resynced.

Place a Member of vSAN Cluster in Maintenance Mode

Bob

[sk84]

vSAN has an option called "Ensure accessibility" for maintenance mode. This ensures that all virtual machines remain accessible when a node no longer participates in the vSAN cluster. Theoretically, nothing should happen if you choose this option. But that would be too hot for me. I would definitely wait until the resync is done. And probably the host won't finish entering maintenance mode completely while the resync is running.

But with the vSAN size and a timeframe of only 30 minutes, 14 days is unusually long. Above all, the vSAN cluster will also start the rebuild after 60 minutes if the host stays in MM, since the vSAN cluster assumes that this node will not come back. Then, the question is what is completed first, the rebuild or the resync.

I would therefore first investigate why the resynchronization takes so long, because this should not be the case and can be a problem again in the future.

Do you see any congestion warnings at the vSAN health checks? Are your NICs saturated or is the network heavily utilized? Is it a vSAN Ready Node configuration? Is NIOC enabled and configured? What's your disk setup like?

[fifthman_roshan]

Thank you very much for that information. It has helped a lot.

[fifthman_roshan]

Thank you very much for that information. It has helped a lot.