vSAN1

Does VSAN does object resync when we choose 'Ensure Accessibility' while putting a ESXi host into maintenance mode. Looks like VSAN is resynching when I choose 'Ensure Accessibility' and it takes more than 5hrs to resync a large repository VM in that data store. But I was thinking VSAN shouldn't do a resync for this option, even it does resyc it shouldn't start for 60mins when components stays as 'Absent'. Missing anything here ?

Hi, a resync/component rebuild process typically depends on your FTT value, if you are using an FTT of 0, then the cluster will need to rebuild the components it will be missing on the remaining cluster hosts to allow the VMs to continue to operate, however an FTT of 1 or more usually doesn't involve any sort of resync process.

We are using FTT=1, but even then resyc starts right away when host puts in to MM.

My experience and I think is by design, is that when you put the host in MM and "ensure accessibility" is set, data is not transmitted to the host so when it comes out of MM it will need to resync. That is my personal experience but I do believe that's how it is supposed to work.

I will second this.  Putting a host into maintenance mode with ensure accessibility should not do a resync, but when it comes back up after reboot it will resync.  Thank you, Zach.

What you will notice is that components on the disks on the host that is placed into maintenance mode (with ensure accessibility) are marked as absent.

This means that they are no longer getting updates - this is a difference between VSAN 5.5 and 6.x - http://cormachogan.com/2015/03/30/vsan-6-0-part-6-maintenance-mode-changes/

When the host is taken out of maintenance mode, then this data will need to sync with the changed data. Depending on how much data has changed, this can indeed take many hours. You should be able to monitor this in the resync view.