1 Reply Latest reply on Apr 20, 2019 3:41 PM by TheBobkin

    Clarification of usable Storage x RAW Storage vSAN

    sandroalvesbrasil Novice

      Hello,

       

      in fact we have no problem, but a doubt.

       

      Shows in the free space of the datastore named as vxRail a free space of 27TB.

       

      In fact, that's the sum of all my HDD drives.

       

      The vSAN calculator says usable Storage is 9.4TB.

       

      We already use 6.49TB.

       

      - Storage Free 21.43TB / Used: 6.49TB / Capacity: 27.92TB

       

      Configuration of the 3 nodes of the vSAN cluster:

      1820 GB x 5 (HDD)

      372 GB x 2 (SSD)

       

      Raw Storage: 1820 x 15 = 27TB

      Usable Storage: 9.4TB.

       

      Doubt:

       

      1 - I know we can not use the 27.92TB, but if we create new VMs the space will be used.

       

      - Why VMware shows RAW space (27.92TB) instead of just showing usable space (9.4TB)?

      - Can we block the use of space above the usable vSAN (9.4TB)?

      - Will any alarms be generated when near the usable space (9.4TB)?

      - If we go beyond the usable space? Will this cause what kind of problem for my environment?

       

      2 - Can you explain to me how vSAN does this 9.4TB calculation?

       

       

      Thank you.

        • 1. Re: Clarification of usable Storage x RAW Storage vSAN
          TheBobkin Virtuoso
          vExpertVMware Employees

          Hello sandroalvesbrasil,

           

           

          "- Why VMware shows RAW space (27.92TB) instead of just showing usable space (9.4TB)?"

          Because multiple different Storage Policies can be applied to different Objects e.g. some data could be stored as FTT=0 and some data as FTT=1 (and obviously far more possible variations in larger and All-Flash clusters).

           

          "- Can we block the use of space above the usable vSAN (9.4TB)?"

          Unfortunately I am not presently up to speed on what ended up being implemented in 6.7 U2 with regard to 'guard-rails' but there are/were plans to start limiting things such as VM creation past certain thresholds. Either way though, from a administrator perspective there is no real control over "blocking" space.

           

          "- Will any alarms be generated when near the usable space (9.4TB)?"

          Yes, you will start getting warnings in vSAN Health once any individual disk passes 80% full and it starts rebalancing this data to other disks where possible:

          VMware Knowledge Base

           

          "- If we go beyond the usable space? Will this cause what kind of problem for my environment?"

          Like any storage system, the VMs need to be able to write to disk - if you run out of space on disks where these components reside then of course the VM will not be functional until space is freed up/rebalanced and it can write to disk. Obviously the solution to this is to size your environment accordingly and not run out of space.

           

          "2 - Can you explain to me how vSAN does this 9.4TB calculation?"

          It is very likely factoring in VMwares recommendation of allowing 25-30% slack space for temporary increases in used space (e.g. changing Storage Policy structure and of course snapshot-data during back-ups).

           

           

          Bob

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