BTRFS and DM-Multpath?

[alex.talmage]

Hi,

We're using DM-Multipath for redundant connection to a disk array on an Ubuntu 16.04. BTRFS filesystem has been installed on the array and we're having issues backing up the volume (support case 04028218).

Support have told me that this is an unsupported setup, quoting:

"Unfortunately, Btrfs is supported only if it resides directly on a physical device with no additional abstraction layers (such as LVM, software RAID, dm-crypt and so on) below or above it.
https://helpcenter.veeam.com/archive/ag ... ments.html"

As its not actually named, I just wanted to check whether BTRFS and DM-Multipath is an unsupported setup?

[HannesK]

Hello,

By utilizing device-mapper, the multipathd daemon provides[...]

"device-mapper" is an abstraction layer covered by "and so on"

I don't know what amount of data you want to backup, but maybe file level backup could help. Or NAS backup.

Best regards,
Hannes

[alex.talmage]

Thanks for the confirmation Hannes, just wanted to be certain it was covered by the "and so on".

We're working to remove the abstraction layer for the time being, as it will likely be around 40TB of mixed file types, so volume backup is our best option I believe.

[HannesK]

yep, you don't want to backup 40 TB file based... I would also think about changing the file system... from BTRFS to something that is fully supported (including multipathing)

[PTide]

Hi @alex.talmage,

I talked to the team and the issue in your support case is very unlikely to have been caused by multipath. However, that hypothesis has yet to be confirmed.

I also encourage you to try file-level mode as it has received a massive upgrade in v4.

Thanks!

[alex.talmage]

I'm still waiting for a change window to remove multipath and run the BTRFS backup again. I'll report back once I've managed to try that.

We will be upgrading to B&R10/VAL4 over the next month or so, again I'll report back what I find.

Cheers,
Alex

[alex.talmage]

Hi All,

So a month on and we've removed dm-multipath from the equation, so just plain BTRFS volume. We've also upgraded to B&R10 and hence VAL4. Getting the same problem.

The job hangs at 99% seemingly doing nothing for a long time (currently 160 hours and counting). Support believe Veeam is having issues removing the BTRFS snapshot and recommending a kernel upgrade. We're going to do this next weekend but I'm not holding out much hope of it fixing the issue as the kernel really isn't that old:

4.4.0-171-generic #200-Ubuntu SMP Tue Dec 3 11:04:55 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

it looks like the most recent for ubuntu 16.04 is 4.4.0.177.18.

Any ideas what I might be doing wrong here? We pushed for using VAL for this new Linux system backups so that we could keep everything together to simplify our job, retention policies, etc rather than having to get a new tool. The Linux team are pushing back now saying its not fit for purpose which is a shame.

Current support ticket is 04094003