vSphere 6.5 virtual NVMe does not support TRIM/UNMAP/Deallocate

Update 2018.10.15

It works more-less fine in 6.7. Known issues/notes so far:

  • Ugly warning/errors is Linux kernel log if Discard is blocked (snapshot create/commit) – harmless
  • Linux NVMe controller has a default timeout of 30s. With VMTools, only SCSI gets increase to 180s so you might want to manually increase nvme module timeout just in case. “CRAZY FAST, CRAZY LOW LATENCY!!!” you scream? Well fabrics and transport layers still may have hickups and tolerating transient issues might be better than being broken.
  • When increasing VMDK sizes, Linux NVME driver doesn’t notice namespace resize. Newer kernels (4.9+ ?) have configuration device to rescan, older require VM reboot
  • One VMFS6 locking issue that may or not be related to vNVME. Will update if I remember to (or get feedback from VMware).
  • It seems to be VERY slightly faster and have VERY slightly lower CPU overhead. It’s within the margin of error, in real life it’s basically the same as PVSCSI.
  • The nice thing is that it works with Windows 7 and Windows 2008 R2! Remember that they don’t support SCSI UNMAP. However NVME Discard seems to work. Delete reclaims space, (ironically) manual defrag frees space, also sdelete zero successfully reclaims space.

I was playing with guest TRIM/UNMAP the other day and looked at new shiny virtual NVMe controller. While it would not help much in my workloads, cutting overhead never hurts. So I tried to do “defrag /L” in VM and it return that device doesn’t support it.

So I looked up release notes. Virtual NVMe device: “Supports NVMe Specification v1.0e mandatory admin and I/O commands”.

The thing is that NVMe part that deals with Deallocate (ATA TRIM/SCSI UNMAP in NVMe-speak) is optional. So back to pvscsi for space savings…

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