Newly created datadevs not immediately available for allocations

Question

I created 95 datadevs (relatively large - 139GB, R5 3+1 ) and I added them to Thin pool. I immediately started pool rebalance and the new datadevs were not getting any new allocations.

What I now understand after talking to the L3 is that there is a background process PHCO/IVTOC that runs on the new devices and before that process is finished, they are not available for allocations. My questions are:

- Do I have a way to estimate when this process will finish, or monitor it ? If I was in situation of pool running out of space, and I needed to allocate space immediately, this would be very unpleasant surprise.

- After the PHCO/IVTOC is finished, does pool re-balance start on it immediately or the re-balance need to be restarted.

- While the device is doing PHCO/IVTOC , is the whole device not available of only the parts of it ? Does it make sense to create more small datadevs vs. less larger datadevs ?

- I understand that this is slow background process, is this process accelerated in any way if the pool is full ?

- If I these were traditional volumes, how does the PHCO/IVTOC affect availability of these volumes, if it was immediately presented to a host.

VMAX20K / 5876.268.174 + fix 68694

M_Salem · Answer

Hi Burhan,

Thanks for contacting EMC Community

I am really sorry to hear that you have this issue. There is a fix# 68779 available for 5876.268.174 that will give high priority for PHCO over normal IVTOC.

PHCO is mainly a security feature introduced in 5876.229 that will make the ucode run a scan on all newly added TDATs to check if they degraded due to a disk failure in the RAID group or so. DAs should scan the devices and once the scan is complete, It clears the PHCO flag and then devices will be eligable for new extents allocation.

To be honest with you, The scan takes some time. There is a way to disable it (Senior PSE is needed for this) but ususally PSE lab discourages doing so, however after adding the fix mentioned above, PHCO is giving very high priority so the scan should take less time.

Like you said, it obviously depends on the size of the TDATs and the number of newly added TDATs to the pool.

Kindly check EMC KB articles

https://support.emc.com/kb/165917

https://support.emc.com/kb/172072

Hope that helps

Mohammed Salem

bhalilov1 · Answer

Fix 68779 is installed - doesn't seem to have helped - datadevs created yesterday were still not available after 24 hours PSE Lab is doing ECBB scans manually

VMAX

Newly created datadevs not immediately available for allocations

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