2 Replies Latest reply on May 20, 2020 4:52 PM by SamWiseTx

    Is it possible to reconfigure VSAN disk groups without downtime?

    SamWiseTx Novice

      Hello everyone. Hope everyone is staying safe.

      I am looking to find a way to reconfigure my VSAN disk groups with the least downtime possible.    

       

      I have a 3 Node cluster. Each cluster has 2 500 GB flash drives and 7 SAS capacity drives.

       

      Recently i started digging on my VSAN config disk groups and noticed that I am only USING one Disk group on each host with 1 SSD and 7 Capacity.

       

      I wanted to know if i would create instead 2 Disk groups on each host would improve performance.

       

      My goal is to have 2 disk groups on each host. (First Group 1 SSD and 4 drives. Second group 1SSD with 3 drives)

       

      I am new to VSAN  and do not know if this new configuration would perform better and if its possible to do this with now downtime.

       

      Also would having 2 disk groups and same amount of capacity disk would that leave me with same datastore size?

       

      Thank you

       

      Sam

        • 1. Re: Is it possible to reconfigure VSAN disk groups without downtime?
          TheBobkin Virtuoso
          VMware EmployeesvExpert

          Hello Sam,

           

          Welcome to vSAN.

           

          "I wanted to know if i would create instead 2 Disk groups on each host would improve performance."

          Yes, likely significantly as you will have double the cache to capacity ratio you have now.

          Whether this will be significantly noticeable depends on whether you are currently pushing the current configuration to near the limits of its capabilities.

           

          "if its possible to do this with now downtime."

          Yes, it is possible without downtime and quite straight-forward:

          1. Ensure you have enough space to comfortably evacuate one Capacity-tier disk - as it is a 3-node cluster, assuming everything is stored as FTT=1,FTM=RAID1 (the default) you would need to have enough available space on a single node (as that is the only valid location for placement of components from the disk you are evacuating because it can't move them to the other nodes as that would violate the Storage Policy). If you don't have enough space (on each node) to remove a disk with 'Full Data Evacuation' option then you can use 'Ensure Accessibility' option though note that some data will be FTT=0 until it is resynced back to FTT=1 so ensure you have good backups.

          2. Remove 1 Capacity-tier disk from a Disk-Group with whichever option is viable.

          3. Create second Disk-Group using your unused Cache-tier SSD and the newly blanked Capacity-tier disk.

          4. Proceed to the same for the next 2 disks on this node, adding them to the new Disk-Group - if you didn't have enough space for it with the 1st disk, you should actually be able to remove each one after the first with 'Full Data Evacuation' option as the data will be able to be moved to the new Disk-Group.

          5. Proceed to do the same for the other nodes.

           

          "Also would having 2 disk groups and same amount of capacity disk would that leave me with same datastore size?"

          Yes. The only time this may not hold true would be if deduplication was enabled (as by the law of odds, you would get a lower dedupe ratio with less data on each Disk-Group).

           

          Bob

          • 2. Re: Is it possible to reconfigure VSAN disk groups without downtime?
            SamWiseTx Novice

            That is great bob. I think I got all the info.

             

            Whether this will be significantly noticeable depends on whether you are currently pushing the current configuration to near the limits of its capabilities.

            I do not think I am pushing near limits but lately I do notice more alerts on my vsan. Also i am planning an installation of some additional new servers that do require good disk performance (SQL and APP server)

            I am at 60% used space but I thought going this route would let me improve cache disk speed as well as no need to buy new capacity drives.

             

             

            Yes my current Vsan policy is the Default - RAID 1

             

            I do have still plenty of space.

             

            Thank you Bob.