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  • 1.  vSAN Memory consumption - are you kidding me

    Posted Sep 18, 2017 02:36 PM

    hello all

    i need to open a question here (in vcenter i opened one for the memory consumption of the ESX). i found out that before activating the vSAN the esx host consumed 1.5 gb ram, after activate the vSAN the hosts consumes 12 gb. i have a testcluster with 3 hosts (for training and learning purpose) in trial mode. as you maybe understand i do not have teras of memory in a test system. i have 16 gb / each host.

    capacity is 47.7 gb

    used 35.58 gb

    free 12.12 gb

    sorry guys, but i am not used that vmware take an example from microsoft and offers memory intense applications.

    is there any possibility to reduced the 10 gb ?

    just for curiosity - what happen in the 10 gb ? what exactly are the 10 gb needed ? what does the option vSAN to the ram ?

    thx guys

  • 2.  RE: vSAN Memory consumption - are you kidding me

    Posted Sep 18, 2017 03:39 PM

    Hello Pille66,

    vSAN has memory-overhead for disk-groups.

    The amount of memory consumed depends on the size and number of disks/disk-groups and whether this is All-Flash or Hybrid:



    To reduce this, consider using less or smaller disks.


  • 3.  RE: vSAN Memory consumption - are you kidding me

    Posted Sep 18, 2017 04:46 PM

    seriously ?

    Example 4: Three disk groups per host, all flash configuration:

    BaseConsumption +

    (NumDiskGroups x

    (DiskGroupBaseConsumption + ( SSDMemOverheadPerGB  x SSDSize)))

    3GB   +    (3   x     (500MB   +    (7MB    x    400)))

    3GB   +    (3   x     (500MB + 2800MB)

    3GB   +    (3   x     (3.3GB)

    3GB   +   9.9GB

    = 12.9 GB

    it matches

    i got 1 ssd (flash drive with 256gb) and 1 flash with 700 gb (datastorage) per host (root storage not mentioned)

    so it means - i need to buy memory

    does it mean if i use a 4 tb datastorage + 512gb flash i would need 28 gb ram ?

  • 4.  RE: vSAN Memory consumption - are you kidding me
    Best Answer

    Posted Sep 18, 2017 05:11 PM

    Hello Pille66,

    "seriously ?"

    Unfortunately yes, sorry to see that you only found out about it at this stage.


    BaseConsumption +

    (NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +

    (NumCapacityDisks * CapacityDiskBaseConsumption)

    In your case this adds up to approximately the consumption you have observed:

    5426 MB + (1 * (636 MB + (14MB * 256))) + (1 * 70 MB)

    5426 MB + (1 * (636 MB + (3584))) + (70)


    9,716 MB

    For 512GB Cache-tier:

    5426 MB + (1 * (636 MB + (14MB * 512))) + (1 * 70 MB)

    5426 MB + (1 * (636 MB + (7168))) + (70)


    13,300 MB

    You would likely do okay with a 256GB cache-tier SSD for a 4TB All Flash disk-group.


  • 5.  RE: vSAN Memory consumption - are you kidding me

    Posted Sep 18, 2017 05:42 PM


    the 256gb version i just use because i had it here. as i told, its a test system and i use what i have

    to give my learning experience more pleasure i get some 128 gb for the 2 tb now

    something else

    as i understand, to the vSAN config it can be added hosts without storage only cpu and Ram. it mean 3 x proz, ram, storage + 3 x proz and ram

    does the calculation match for the added hosts without storage (except the root) too - it would mean round about 5 gb per host

    thx so far

    was very helpfully input

  • 6.  RE: vSAN Memory consumption - are you kidding me

    Posted Sep 18, 2017 06:24 PM

    Hello Pille66,

    The calculations above are for one host with one (All Flash) disk-group with one capacity drive - the memory overhead is consumed by this node alone. Nodes without disk-groups would not incur any disk-group related memory overhead.

    Yes, it is possible to have 'compute-only' nodes in cluster, though 3 nodes with storage is the minimum to use the basic range of functionality that vSAN offers. For instance, it is technically feasible to make a 1-node vSAN 'cluster' but it would only be able to create FTT=0 Objects, this would be the same case if you had only one node with storage.