Failing server, will CU 16 and CU 21 mismatch be an issue

Have a failing cluster disk with an Exchange 2013 CU16 Std VM on it. Pool will not rebuild on new disk and will only attach if the failing disk is in the array.

Storage was reporting no errors and only found due to failing backups, so backups are not current.

I have decided to install a new Exchange box and attempt to move the mailboxes. Issue is I onlu had access to Exchange 2013 SP1 and CU21 and the failing server is CU16 which is not available.

I do not want to even think about attempt installing CU21 on the failing space. My question is whether it is advisable or is a problem to install CU21 on the new machine and migrate the mailboxes with the version mismatch.

I am stuck, storage will not stay stable for backups, VM moves, or even attempting to copy the vhdx. I know the mailbox moves are high I/O but I don't seem to have a choice to to attempt it.

Will the 16 - 21mismatch be a problem?

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timgreen7077Exchange EngineerCommented:
The CU versions dont have to be the same, and you can still move mailboxes even though the CU versions are different.

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ccroasmunAuthor Commented:
I really appreciate it, been hanging on a thread here. Thanks for the quick response, wanted to move forward tonight and now I can.
Even though its  going to work but would highly recommend to be on the same version as in case something happens worst you would be on un supported platform.
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andyalderSaggar maker's framemakerCommented:
...not rebuild on new disk and will only attach if the failing disk is in the array.

As a matter of interest is it an HPE ProLiant?
ccroasmunAuthor Commented:
Yes Andy it is Proliant
ccroasmunAuthor Commented:
Thanks Pradiip, that's why I posted, I new this is not best practice and wanted to ensre that the CU mismatch may include attribute additions etc that may cause issues during the move, thus Microsoft best practice of not running mismatched. In this case I don't want to touch the degraded box with anything like a CU install in fear of losing it entirely.
andyalderSaggar maker's framemakerCommented:
Pound to a penny you changed the wrong disk. the big rectangular button that lights up red is the "do not remove" light. The actual status lights are tiny in comparison. See the bottom of

HP claimed it is not red but "port wine" coloured, I claim it's the most stupid design ever.
ccroasmunAuthor Commented:
This could be possible, but in a round about way. The week before I had a drive light go red, that drive I replaced and rebuild completged successfully. Backups had already been failing before this drive indicated red, and I had been troubleshooting both on the server side and Veeam without being able to isolate the issue previously to that drive going red.

After the successful rebuild, backups were failing at the same exact spot 13.8 GB processed, as they were before the mysterious red light "failure". I continued looking for issues and found many articles indicating Storage Spaces not properly reporting drive level errors.

When interrogating the physical drives I found another drive that was reporting several hundred thousand uncorrected errors. I retired this drive of which indicated no issues throughout the Spaces stack, nothing on the pool, cluster disk, volume, etc.

It is the replacement of this second drive that has failed. It seems plausible that it was always the actual problem and I may have replaced the "red bllnky" and repaired across the actual bad drive. This may have been what caused this to get so bad.
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