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  • 1.  vSAN (Storage) Policy Configuration

    Posted Jun 30, 2017 10:38 AM

    I have a question regaring policies in a typical Horizon View environment.

    We have a 10 hybrid hosts vSAN cluster (per hosts 2 SSD's 10 Spinning disk, 2 disk groups per host 1/5)

    vSAN Default Storage Policy is:

    FTT=1

    Disk Stripes : 1

    Then, we have Horizon View 6.2 which automatically creates vSAN Storage Policies.

    For the VM_Home policy :

    FTT=1

    Disk Stripes : 1

    For the OS_DISK_Floating (the linked clones), we have:

    FTT=0

    Disk Stripes : 1

    Ok, that results in a broken VM whenever a disk fails (been there done that :smileyhappy: )

    We are going to fix that, but!


    Nowhere is FTM configured.

    Should we do that?

    If yes, why should we do that?

    If yes, where should we do that (only default vsan policy, or everywhere)

    I guess everything is RAID 0, we have VM's with an other policy with:

    FTT=1

    Disk Stripes=1

    We have had disk failures and these VM's are not affected...

    Thanks!



  • 2.  RE: vSAN (Storage) Policy Configuration

    Posted Jun 30, 2017 07:58 PM


  • 3.  RE: vSAN (Storage) Policy Configuration

    Posted Jul 13, 2017 10:23 PM

    The Failure Tolerance Method rule for Hybrid configurations can only be RAID1/Mirroring.

    Number of Failures to Tolerate rule determines how many failures an object may have.

    The OS disk for your Linked Clones being set to FTT=0, means there is only ever 1 copy of the OS disk. We would suggest that this is FTT=1.

    Horizon View 6.2 and other versions have defaulted to FTT=0 in some cases. This is corrected (I believe) in Horizon View 7.0 (or maybe a later release).

    You may set a policy to FTT=1 (1 copy/survive 1 failure) and FTM=Mirroring/RAID1 if you wish to prevent the loss of the OS Disk as you mention.



  • 4.  RE: vSAN (Storage) Policy Configuration

    Posted Jul 14, 2017 12:48 PM

    Hi Jasem,

    Thanks for your feedback, one thing I don't understand ....

    Why FTT & FTM... why is only FTT=1 on a VM not enough then?
    What would be the sum when enable FTM and FTT...

    Thanks!



  • 5.  RE: vSAN (Storage) Policy Configuration

    Posted Jul 14, 2017 02:04 PM

    Hello Johan,

    Just to clarify here:

    Failures To Tolerate (FTT) is the specification of how many copies of data components that can be unavailable and the Object still functional.

    e.g. FTT=1 Objects will be accessible after the loss of a single host or a disk/disk-group that its components reside on.

    Fault Tolerance Method (FTM) specifies the method by which this FTT is applied.

    e.g. if you had All-Flash you could apply RAID5 instead of RAID1, BOTH of these provide FTT=1 protection to the Objects but how they do it different (R1 uses 2 mirrored data components, R5 uses 3 smaller data components + parity).

    As you can only use RAID1 for FTM here, changing Objects from FTT=0 to FTT=1 will use 2x space these Objects currently use on the vSAN Datastore (while if you could use RAID5 this would only be 1.33x but with write penalty).

    In short, if you are using Hybrid then you can ignore the FTM option here.

    Bob



  • 6.  RE: vSAN (Storage) Policy Configuration

    Posted Jul 14, 2017 02:33 PM

    Thanks!

    Clear!