VMware vSphere

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  • 1.  Number of VMs per datastore

    Posted May 06, 2022 07:17 PM

    On ESXi 6.7 and 7, is there a guideline for how many VMs per datastore? I've tried to search, but I am not find anything very current.  I know the old recommendations from like 10+ years ago was about 15-25 depending on activity due to things like SCSI locks, queue depth and reservations.  That's what I've been still going by, and usually try not to exceed 25.   I've had some with 30-35 for a little while until I could rebalance, and they have been OK.   

    Problem is, that we have hundreds of VMs, so spreading them out amongst dozens of datastores to keep the counts at 25 does become a bit of administration overhead and often makes for space silos.  Maybe you will need space, but the only datastores that have a bunch of free space already have a lot of small VMs on them, for example.  I'm getting some pushback from some on my team who think we should just make a few huge datastores and fill them with 100s of VMs each, which seems like a bad idea to me, but maybe my training is just outdated. 

    Just wondering if there is an official recommendation or what other people are doing.   

    We are running two different SAN, one on 16GB FC and another on 10Gb iSCSI, both are very fast storage.   

    Thanks in advance.  

  • 2.  RE: Number of VMs per datastore

    Posted May 06, 2022 09:34 PM

    Disclaimer: this is a biased point of view - my daily job is to recover VMs from corrupt datastores.

    Questions you have to answer first:
    1. do you replicate your datastores regularly - does this really work ???
    2. do you backup your VMs daily - does this really work ???

    Assume one of your datastores fails - can you be back in production over the weekend ? - or do you rather need a whole week ?
    In my point of view the number of VMs is less relevant than the size of your datastores.
    A datastore that is so large that replacing / rebuilding takes a week is IMHO a bad idea - a really bad idea.

    All parameters you mentioned like SCSI locks, queue depth and reservations may cause minor complaints.
    If a recovery takes a week or longer it can result in a business desaster !

    My recommendation: a datastore that you cant replace / rebuild over the weekend is too large.