CBT reset still required?

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CBT reset still required?

Veeam Logoby timmi2704 » Wed Jul 19, 2017 2:27 pm

Hi forum!

I was just wondering, whether the CBT reset after a disk size change is still required (vSphere environment).
As far as I know, this behaviour was implemented as a workaround to a nasty VMware bug.
According to our technical contact at VMware this is not neccessary any more with the latest vSphere 6.5 release.
Is there any further information on this?

Thanks for that :D
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Re: CBT reset still required?

Veeam Logoby Gostev » Wed Jul 19, 2017 3:33 pm

Correct, not required.
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Re: CBT reset still required?

Veeam Logoby JoshuaPostSAMC » Wed Jul 19, 2017 7:13 pm

Gostev, that should apply to even 5.5 as long as it has the update to correct the problem, right?

In that case, we can change the registry setting so Veeam stops resetting CBT
https://www.veeam.com/kb1940

──────────────────────────────────────────────────────────
Veeam Backup & Replication v8 and Later
──────────────────────────────────────────────────────────

Veeam Backup and Replication 8 has a built-in solution for this issue. Veeam Backup & Replication resets CBT for any resized VMware disk to prevent corruption. If ESXi hosts are patched against this issue, this behavior may no longer be desirable. To disable automatic CBT reset upon virtual disk size change, create the following registry value on the Veeam Backup Server (requires v8 Update 2 or later):

Key: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication
Type: REG_DWORD
Value name: ResetCBTOnDiskResize

Set this DWORD value to 0. To apply the registry change, make sure no jobs or restores are running, then restart the Veeam Backup Service.
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Re: CBT reset still required?

Veeam Logoby timmi2704 » Thu Jul 20, 2017 4:05 pm

Efficiency at its best!
Thanks Anton, thanks Joshua. RegKey is set.

Maybe B&R will detect current patch level and reset CBT only if really neccessary some day ;)
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Re: CBT reset still required?

Veeam Logoby Frosty » Mon May 21, 2018 11:51 pm

Am just completing the build of our new Veeam-based backups environment, and I found this note from when we updated our old setup to VBR 8.0:

As part of the upgrade to VBR v8.0 the following Registry Key was created:
HKLM\Software\Veeam\Veeam Backup and Replication
ResetCBTOnDiskResize (REG_DWORD) = 0

Having read up on this and having found this thread, I've concluded:
(a) that if we do set this registry key, backups will be more efficient in cases where we resize a disk; but
(b) we might NOT want to set this key, so that in the event that some oddball CBT issue reappears in vSphere, we'll be better protected

I'm thinking to not bother adding this key. I prefer safety and reliability over performance.
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Re: CBT reset still required?

Veeam Logoby Gostev » Wed May 23, 2018 12:28 pm

Not a bad choice. I mean, how often do we resize those disks anyway :D
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