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Would it be possible to have DRBD directly running inside a Ceph Pool?

I have a backup machine with files stored directly on disk. The offsite backup machine has Ceph installed and configured on all the disks.

I would like to have a second replica of the backup data on the offsite backup machine, but I'm a bit confused at which 'layers' DRBD and Ceph operate. Would it be possible to create a RBD pool at the offsite backup machine and configure DRBD directly on that or, do I need to go the route where I run a virtual machine using Ceph and configure DRBD in the virtual machine as a abstraction layer?

Edit:

The reason the (single node) offsite backup machine is running Ceph is because it is mirroring the pools of a (multi node) main Ceph cluster.

In addition to the main Ceph cluster we have a backup server creating file backups of the machines running on the cluster. This is a simple RAID5 configuration where the data is stored on.

To have a extra copy of the backup data I also want to sync it, using DRBD so that I do not have a problem with small files, to the offsite backup machine. But as the disks of the backup machine are already configured to be a Ceph OSD I need to store it somehow on in a Ceph pool.

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  • I'm not sure I fully understand your question. If you have a running ceph cluster you can use three different protocols, RBD, CephFS or S3. A mapped RBD device is like a physical disk for the client, so you could simply map an RBD image from ceph on your backup machine and sync your backup files to the new device. If you have CephFS running, you can just mount it on your client and sync your backup files into the filesystem. S3 probably won't apply here. If your ceph cluster is configured properly you'll have redundancy so there's no real need for DRBD. Or is it required to use DRBD?
    – eblock
    Feb 15, 2023 at 8:28
  • Do I understand correctly that you have only one ceph machine? That's usually not the best idea, you have no failure resiliency.
    – eblock
    Feb 15, 2023 at 8:29
  • Hi @eblock, I understand your concern about the 'one' Ceph machine. I have updated the question in the hope it will make it a little bit more clear.
    – Mr. Diba
    Feb 15, 2023 at 8:57

1 Answer 1

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Yes it is possible to run a DRBD inside a Ceph pool using RBD.

Using the steps from https://docs.ceph.com/en/latest/start/quick-rbd/

First create a block device pool and initialize the pool to be used by RBD, lets say the pool name is called backuppool

rbd pool init backuppool

After that create a block device image:

rbd create foo --size 1G backuppool/backup-drbd

Using the magic commando rbd map backuppool/backup-drbd the device gets mapped on the host as /dev/rbd/backuppool/backup-drbd.

After that is is possible to configure DRBD as normal, selecting the /dev/rbd/backuppool/backup-drbd disk as disk in the DRBD configuration.

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