vSphere 6.5 U2

Last week VMware released vSphere 6.5 U2 in the midst of Dell Tech World so I didn’t have a chance to post this. Normally I don’t call out individual updates for vSphere, but this one contains an important fix to UNMAP that one of our customers discovered. The issue occurs only when attempting to run a manual UNMAP in the following environment:

  • vSphere 6.5
  • VMFS 6
  • zeroedthick or eagerzeroedthick vmdks

As you can see it does not impact thin vmdks or VMFS 5, nor automated UNMAP. So how do you know if you have the problem? Basically when you run the esxcli storage vmfs unmap command, it finishes quite quickly and very little storage is reclaimed. If you are monitoring VAAI stats you will also see few UNMAP commands issued.

So why is VMware not issuing enough UNMAPs? Well internally to the VMFS there are two types of filesystem blocks – large (LFBs – 512MB) and small (SFBs – 1MB). In vSphere 6.5 on VMFS 6, VMware is not processing LFBs – the majority of blocks. Since thin vmdks are all SFBs, this bug does not impact them.

Fortunately, as this bug was identified before vSphere 6.7 was in final RTM, we managed to get it added to the GA release of that so you could apply U2 or upgrade to 6.7. Obviously if you use automated UNMAP only or thin vmdks the individual fix is unnecessary, but U2 does have lots of other fixes. This particular bug is shown in the fixed issues of the release notes. It’s always best practice to apply the updates to vSphere as they are roll-ups and have both functional and security fixes.



5 thoughts on “vSphere 6.5 U2

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  1. Hi Drew,

    Months ago, I met the similar issue like you mentioned above.

    My issue is as below:
    a. ESXi 6.5 +VMFS6 (Auto UNMAP enabled)
    b. Delete VMs directly or delete VMDK
    c. Issue a manual UNMAP command
    d. No unmap commands sent to array from ESXI

    I’m not aware of that format of vmdk might impact.
    After troubelshooting with VMware support, VMware gave me a conclusion that manual unmap is not support on auto unmap enabled VMFS6 datastore.

    But it seems that it’s not true according to your artical.
    Do you have more details of this defect you mentioned in this artical?

    Thank you very much!

    1. I tested the fix myself. It works for VMAX. I’ll find out why VMware has this in the RN. Perhaps they are concerned about a corner case or another array type since I think I am the only one who tested it.

    2. So first, manual UNMAP is and always was supported on VMFS 6. Don’t know why VMware told you that but they were wrong. This particular bug was real, however, so you probably were not using thin vmdks and hit the issue. As I noted in the post it is fixed in 6.5 U2 and what I found out about the Release Notes is they put it in there as a known issue early on in the doc process when development alerted them to our problem. After it was resolved and added to U2, someone forgot to remove it so we are looking to get the RN corrected.

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