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  • 1.  vSAN Stretched Cluster Capacity Meter

    Posted Mar 31, 2023 01:26 PM

    I have a question related to the "vSAN Capacity Meter" under Cluster > Monitor > vSAN > Capacity and how it relates to a vSAN stretched cluster deployment.

    My understanding is: vSAN is a cluster level construct and capacity is viewed logically at the cluster level. So if we are looking at capacity from a vSAN stretched cluster point of view, this is the capacity that the entire system has for both sites (combined).

    Screenshot 2023-03-31 at 15.19.22.png

    So my question is this... ideally we should try to keep capacity to under 50% of this meter. As this is a stretched cluster, one of the main use cases is having a solution that can withstand / mitigate an entire site failure. If we lost one of the sites... the one surviving site would host all of the storage (goes from 50 to 100%).

    Is this correct?



  • 2.  RE: vSAN Stretched Cluster Capacity Meter
    Best Answer

    Posted Mar 31, 2023 03:55 PM

    , No that wouldn't be necessary. The default policy for Stretched cluster is stores data as FTT=1,RAID1 across sites e.g. data-replica on SiteA + data-replica on SiteB + witness component on Witness site.


    So, let's say you had 80% used of the total cluster storage, then you lost SiteA, the data would remain accessible from SiteB (but would be functionally FTT=0), the clusters total capacity would be halfed but the usage at SiteB would still be 80% (of this now lower total amount).


    You should leave enough available capacity on the cluster for growth/increase of vmdk size (as almost everyone stores these as thin-provisioned these days), any additional data that may be moved to the cluster and for any temporary space usage (e.g. snapshots during backups or changes).