CBT

VMWare, as of writing, has a nasty bug that means your backups that run utilising CBT (hint: if you have basically any enterprise backup product worth its salt, it’s got CBT enabled) it loses track of the changed blocks when the VMDK reaches any Power 2 value of 128GB (128, 256, 512, 1024, etc.) which may make your backup unrecoverable. The VMWare bug is in KB: kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2090639 ↗ The remedy for this is to disable and re-enable (reset) CBT on the affected machines, this can be done with the machine powered off or with it turned on by running PowerCLI commands and a snapshot, we will be doing the latter, no one likes downtime ↗:...

Recently had a problem were Veeam was giving bother on one VM that had a dedicated datastore, not allowing hot-add virtual appliance mode to work. I originally thought it was a problem with CBT (changed block tracking) so I disabled that, with no luck, as it transpires there were a few (all datastore formatting related) problems: The Veeam proxy’s datastore was formatted in VFMS-3 with a 2MB block size and upgraded to VMFS-5 (retaining its 2MB block size of course - otherwise a reformat would be needed)....