CBT: the thread to centralize your feedback

Tristis Oris

@rtjdamen but i can't disable CBT globaly? it auto applied to every VDI when been implemented.
Disable CBT for each VDI not required, because it happens automaticaly during migration. I only need to remove all snapshots.

rtjdamen

@Tristis-Oris indeed seems like thats a bug in xoa that it does not delete the snapshots

jon02

@flakpyro
I have the same problem.
I'm on 8.2 as well and have a local ZFS SR.
I'm going to upgrade to 8.3 and look, if it helps.

flakpyro

Another interesting development. In our test environment this week i installed the latest HP Service pack for proliant, doing so required a server reboot so I ran a rolling pool reboot from XOA, later when the test environment backup job kicked off, i noticed it was running a regular Delta despite the migrations that must have occurred during rolling pool reboot.

SSHing onto a host and checking i see sure enough the cbtlog is reporting all zeros...

[17:27 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 73877c18-a5bf-43bb-aaf5-299f46710d7e.cbtlog 
00000000-0000-0000-0000-000000000000

However the backup ran as a delta, running the backup again manually and it is once again it runs as a delta.

Checking after the manual backup the result is not all zeros anymore:

[17:28 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 65d8656e-93e8-4e81-b1a8-0b0462f6fbb8.cbtlog 
1950d6a3-c6a9-4b0c-b79f-068dd44479cc

Now..just for fun i decided to manually migrate a small VM to another host and then back to see what happens:

After the migration back to all zeros:

[17:32 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 65d8656e-93e8-4e81-b1a8-0b0462f6fbb8.cbtlog 
00000000-0000-0000-0000-000000000000

And running a backup manually resulted in the usual error:

Can't do delta with this vdi, transfer will be a full
Can't do delta, will try to get a full stream

So...this just makes the issue even more confusing, why does a rolling pool reboot not cause this behaviour but a manual migration does? Does the ID being all zeros not actually matter? I seem to be able to consistently reproduce this too. Ill be curious to next test if a "rolling pool update" causes this behaviour next time a batch of updates is released.

rtjdamen

@flakpyro very strange issue indeed, we can’t reproduce the problem on our end. So as @olivierlambert mentioned before it has to be something specific. The new developments make it indeed more difficult to understand, but i believe there is a logical explanation to this.

olivierlambert

@flakpyro How do you migrate the VM already? I mean the exact steps you do.

flakpyro

@olivierlambert

In XOA i browse to the VM inventory list, search for the VM i want to migrate, check the box beside it, and click the migrate button located at the top right of the page, the "Migrate VM" popup appears and select the second host which is in the same pool, and click "Ok"

We have 2 pools i can reproduce this on:

The "Test Environment pool" with 2 HP DL325 Gen 10 servers backed by a TrueNAS MINI R running NFS 4.1

Our Production pool running 5 HP DL320 Gen 11 servers backed by a Pure //20R4 running NFS 3.

On the networking side:

Both pools are connected to 2 Aruba CX 10G switches (VSX Stack), each host as 4 physical connections:

2x !0G Bond0: Storage/Management/Backup, MTU 1500, VLANs for VM Traffic/Managemnt/Backup

2 x 10G Bond1: Dedicated storage: MTU 9000, ONLY used for NFS storage traffic on an isolated storage VLAN.

Both the TrueNAS and Pure use MTU 9000 on their "Storage" ports as well. I know Vates steers people away from Jumbo frames as a rule, and i agree but Pure engineering was pretty adamant about using them, so they are only present on these dedicated ports for storage only.

I will soon have a 3rd pool to test on as our DR site comes online next month, it will also be backed by Pure Storage.

I see others are also experiencing this issue as well now, looking at some more recent posts on this thread.

It should be noted regular backups with "NBD and CBT" enabled but with the snapshot deletion button turned off run without issue and have for months now proven themselves reliable. It would just be nice to not have to keep that snapshot daily

olivierlambert

Could you try to migrate with xe and see if you have the same issue?

flakpyro

@olivierlambert

For sure, i ran:

 xe vm-migrate uuid=a14f0ad0-854f-b7a8-de5c-88056100b6c6 host-uuid=c354a202-3b30-486b-9645-2fd713dee85f

To move the VM from host 1 to host 2....

Doing it this way i noticed checking the CBT log file does not result in all zeros being output.

[10:00 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]# cbt-util get -c -n 087ad136-f31b-4d7c-9271-7c926fd51089.cbtlog 
fe6e3edd-4d63-4005-b0f3-932f5f34e036

For fun i then moved the VM back from Host 2 to host 1 and again, the cbtlog file seems to be intact:

[10:02 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]# cbt-util get -c -n 087ad136-f31b-4d7c-9271-7c926fd51089.cbtlog 
fe6e3edd-4d63-4005-b0f3-932f5f34e036

After all this migrating i then ran a job which ran fine and without any errors about not being able to do a delta.

So it seems like it works fine via xe CLI

Update:
After the backup ran properly and generated a new CBT log file i then moved it back and forth between hosts again using the CLI. And the cbtlog file seems to stay in tact again when checking using cbt-util. When i do this with XOA the result from cbtutil is all zeros.

olivierlambert

Okay so back to being an XO issue regarding migration, like if XCP thought it was migrating storage. Ping @julien-f or @MathieuRA

@flakpyro can you provide screenshot on how you migrate with XOA?

flakpyro

@olivierlambert

Here is a screenshot of how i am doing the migration in XOA: moving from host 2 to host 1, leaving the SR drop down empty.

olivierlambert

And when doing that, you are losing the CBT thing (like it's all 00000), right?

And if you unselect everything but the destination host, is it behaving the same?

flakpyro

@olivierlambert
We're making progress i think!

Correct letting the migration run with those settings results in 0000 when running the cbt-check command.

I tried removing the migration network and ran a migration with the following settings:

Screenshot 2024-12-18 at 2.28.44 PM.png

Before migration:

[14:27 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 7560326c-8b15-4c58-841f-6a8f962a7d28.cbtlog 
fe6e3edd-4d63-4005-b0f3-932f5f34e036

And after migration:

[14:27 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 7560326c-8b15-4c58-841f-6a8f962a7d28.cbtlog 
fe6e3edd-4d63-4005-b0f3-932f5f34e036

If i select a default migration network and run the same migration:

[14:31 xcpng-test-01 45e457aa-16f8-41e0-d03d-8201e69638be]#  cbt-util get -c -n 7560326c-8b15-4c58-841f-6a8f962a7d28.cbtlog 
00000000-0000-0000-0000-000000000000

I think we're getting somewhere now! I have the migration network on both the test and DR pools. This used to be our "Vmotion" network back when we ran vsphere and i decided to continue using it to keep migration traffic on an isolated secure vlan.

In fact these Veeam VMs are not even being used anymore they exist in our test lab as VMs to mess around with for things like this.

olivierlambert

So selecting the migration network is like triggering something in XO that makes XCP-ng moving the VDI like it was a storage migration (resetting the CBT status).

Ping @MathieuRA and/or @julien-f

flakpyro

@olivierlambert Glad we're getting to the bottom of this!

Out of curiosity is having an isolated migration network only available to the XCP-NG hosts considered best practice with XCP-NG? It was with VMware to keep VMotion traffic on its own subnet and since the VLAN was already created on our switches i decided to keep with that setup. Ideally we can get this fixed either way, I'm just curious if I'm doing something considered strange?