Flash disks not used VSAN 6.0 U2

[georgemason]

Hi,

We are seeing an issue where flash storage looks to be correctly configured and detected in VSAN, but not used:

Looking a bit deeper, it appears that the NVMe disks aren't eligible due to an existing partition on the disk:

[root@localhost:~] esxcli storage vflash device list

Name                                                                                Size  Is Local  Is Used in vflash  Eligibility

--------------------------------------------------------------------------------  ------  --------  -----------------  ----------------------

t10.NVMe____INTEL_SSDPEDMD800G4_____________________CVFT607600A9800CGN__00000001  763097      true              false  Other partitions exist

The partitions on the disk look like so:

[root@localhost:~] partedUtil getptbl /dev/disks/t10.NVMe____INTEL_SSDPEDMD800G4_____________________CVFT607600A9800CGN__00000001

gpt

97281 255 63 1562824368

1 2048 6143 381CFCCC728811E092EE000C2911D0B2 vsan 0

2 6144 1562824334 77719A0CA4A011E3A47E000C29745A24 virsto 0

Interested to hear comments from other members on what might be causing this? The SSD was never used for any other function.

Thanks

[TheBobkin · Accepted solution]

Hello George,

Those two partitions are vSAN partitions created when the disk-group was created.

Are you wondering why the used space on the NVMe is 0B?

This is because the cache-tier device is not used for storage, it is used to stage and de-stage data from the capacity-tier devices in this disk-group so nothing is permanently stored on this device.

These commands should show you that this is in use by vSAN and the configured purpose:

#vdq -q

#esxcli vsan storage list

(e.g. the cache-tier NVMe will show as "Is Capacity Tier: false" )

Bob

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[georgemason]

Hi Bob

Thanks for your reply, makes sense. So can I take it from that response that there is no way to see how *much* of the SSD is being used? Not that it matters I suppose as it can't be used for anything else, but out of interest it would be good to know.

I had a suspicion that everything was working correctly and glad to hear that is the case!

George

[TheBobkin]

Hello George,

Glad I could help clarify things here.

This won't be a static amount, this is constantly fluctuating as data is staged and de-staged, there *are* means of looking at different usage levels using vsish but this is not trivial. Also there can be other factors on SSDs relating to how much space is really *free* such as Manufacturer-set Over-provisioning and Dynamic over-provisioning.

Bob

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