VMware Cloud Community
microlytix
Enthusiast
Enthusiast
Jump to solution

vSAN stretched cluster and read locality

This is a theoretical question that came up on one of our vSAN classes.

Imagine a VM running on a stretched vSAN-cluster (v7.0.3) with a site disaster tolerance: "site mirroring - stretched cluster" and (local) failures to tolerate: FTT=0.

This VM has one disk copy on the prefered site and one copy on the secondary site. The VM's compute is on a host on the primary site.

Now imagine the disk group with the vmdk breaks down on the prefered site.

Compute is still at the prefered site and all i/o need to go to the secondary site where the last remaining copy of the vmdk is located..

Will the VM vMotion to the secondary site in order to be closer to its disk object or does vSAN wait for a rebuild on the primary site?

I'd guess it's the latter case, but I haven't tried yet (... I didn't dare to kill a disk group in a production cluster). 😉

TIA for your thoughts

Michael

blog: https://www.elasticsky.de/en
Reply
0 Kudos
1 Solution

Accepted Solutions
TheBobkin
Champion
Champion
Jump to solution

@microlytix, (unless there was some change I am unaware of) No it won't vMotion the VM, it will just read from the remaining replica in the other site, start repairing the other replica (assuming it is marked as degraded), then switch to reading from that new local replica once it is active.

 

If you ever want a good smashy smashy place to test failure behaviour, you can always use VMware HOL labs (though the vSAN ones are still on 7.0 U2 currently unfortunately).

View solution in original post

2 Replies
TheBobkin
Champion
Champion
Jump to solution

@microlytix, (unless there was some change I am unaware of) No it won't vMotion the VM, it will just read from the remaining replica in the other site, start repairing the other replica (assuming it is marked as degraded), then switch to reading from that new local replica once it is active.

 

If you ever want a good smashy smashy place to test failure behaviour, you can always use VMware HOL labs (though the vSAN ones are still on 7.0 U2 currently unfortunately).

lukaszzasko
Enthusiast
Enthusiast
Jump to solution

Hi,

No - it will not vMotion to host with remote component. It will wait for fix the problem with local component and in the same time will use components in second site.

Reply
0 Kudos