One disk on VM is not using CBT

[Line_Rider]

I have a file server VM with three disks in which two are backing up with CBT on but the third is not and thus takes 4 hours as it reads through the entire 1.5 TB volume.

• OS - uses CBT on CSV1
  Data1 - uses CBT on CSV2
  Data2 - Not using CBT on CSV1

The OS and Data1 disks are new where the Data2 disk was detached and then attached to this VM, that's the only difference between them. Both Data disks are on the SCSI controller.
I'm considering creating a new .vhdx file from the contents of Data2 or maybe a storage migration to a different CSV but wondering if there were any ideas before I get started on that.

[PTide]

Hi,

Does that occur every tbackup session? Also, is that a Hyper-V cluster where the subject VM resides at?

Thank you.

[Vitaliy S.]

CBT should be enabled on the subsequent job run. Can you please tell us where this disk is located? Is it the same datastore as for other two disks?

[Line_Rider]

Yes this occurs on every run since I started backing up this vm last Friday.
It is a 2012 Hyper-V Cluster with 3 nodes and two CSV volumes.

The VM's disks are on on the separate Cluster Shared Volumes,

CSV1 has the D:\ .vhdx file
CSV2 has the C: and E:\ .vhdx files

C:\ is using [CBT] = 1 minute to backup
D:\ is using [CBT] = 5 minutes to backup
E:\ is NOT using [CBT] = 4.5 hours to backup

This VM is 2012 R2 and newly created a week and a half ago.

The C:\ and D:\ volumes were new created and the content from the old server robocopied over.
The E:\ was attached and in use on the old VM and I detached and then attached it to the new VM.

D:\ and E:\ are on the SCSI controller.

[Vitaliy S.]

What is the exact error message you see for this disk? Does it say that CBT cannot be enabled or something else?

[Line_Rider]

It doesn't show an error, just that it's not listing the [CBT] tag at the end and takes significantly longer than the other disks.

Hard disk 1 (1.0 TB) 4.3 GB read at 65 MB/s [CBT] | Duration is 0:01:28
Hard disk 2 (80.0 GB) 1014.0 MB read at 58 MB/s [CBT] | Duration is 0:00:19
Hard disk 3 (1.5 TB) 815.6 GB read at 49 MB/s | Duration is 4:46:25

[Line_Rider]

I can go through copying the data to a new .vhdx and seeing if that resolves it, but will take the majority of the day I think. I also intend to run an optimization on the file tomorrow.

If I should open a case on this I can do that too.

[Line_Rider]

I ran an optimization on that disk this morning and it didn't shrink or basically anything while the other disks did. Almost like it's behaving as if it's a full disk rather than dynamic. Anyway so I created a new .vhdx and am copying the data from this weirdly behaving disk to that one and will see what happens.

[Vitaliy S.]

Got it, keep us updated on the results after you copy all the data. If the issue still persists, then I would suggest taking a closer look a the storage and host where this disk/VM resides.

[Line_Rider]

I got the data copied to a new disk over the weekend; deduped it yesterday and it compacted properly last night. I ran a full backup aftewards and this evening it will run the incremental. I will know tomorrow.

[Line_Rider]

Well, the new disk with all the data copied is now using CBT and runs an incremental in 5 minutes.

And the other two disks are suddenly not using CBT for no reason at all that I can tell because nothing was changed on those.

The job is now completing in 1 hour which is 3 hours faster than it was before so I'll take it.

[Vitaliy S.]

Let our support engineers take a look at the backup job log to understand what has happened. Once you do this, please post your case ID.

[Line_Rider]

Support case submitted, case ID 01735409