Sync Servers with DRBD

drbdsynchronization

assume if I synchronized two servers and I used DRBD, and after I synced them I installed application on both, if I wanted to add a third server. is that possible? since I think I should create block device and use it in the installation and that is made during configuration of the DRBD on both servers

if yes, is that (add more servers in future) also applicable to NextCloud servers?

Thanks

Best Answer

DRBD 9 can scale to 31 replicas of your data, so 32 nodes. DRBD 8 was limited to 4 nodes through stacking, but it was still possible. You can certainly start with 2 nodes, and then add a third with DRBD 8 or 9.

DRBD is in the mainline Linux kernel, so unless NextCloud is only providing distros that remove DRBD from the kernel, it will be and work there.

There seem to be some misconceptions flying around about DRBD in this thread: You don't need any cluster aware filesystems for DRBD in Active-Passive mode. You would in Active/Active, same as with a shared block device on a SAN. Also, DRBD 9 scales pretty well with up to 32 nodes per cluster, with fancy ways to increase that number.

Related Solutions

DRBD – Experimenting with DRBD and Virtualization

At least with Xen my experience is that it's better to let the Dom0 handle the block devices. I haven't dealt with DRDB but with iSCSI it's better to have Dom0 be the iSCSI initiator and then just have the DomU use the resulting block device.

DRBD doesn't care about the filesystem that's running on the volumes so I would say this is probably best done in the DomO. This also gives you the ability to have DRBD backup Window DomUs.

You may also want to check out this question as it addresses some of your questions about running heartbeat on a vm.

Lvm – DRBD LVM – backed vs. physical & LVM filter

If I understand your requirements correctly, this is what I would be doing:

Create a single DRBD device mark it as a PV for LVM. Create Pacemaker resources for the DRBD volume and each of the LVM logical volumes, with the logical volumes depending on the DRBD volume.
Your pv filter looks correct. Have you verified that the DRBD device is correctly marked as a PV? If it doesn't have metadata on it, it won't show up. Try using the pvck command to verify this:
```
$ sudo pvck /dev/sda1
  Found label on /dev/sda1, sector 1, type=LVM2 001
  Found text metadata area: offset=4096, size=192512
```
You could also try replacing your filter with a/.*/ so it scans every volume. Although unless you've messed with how drbd devices are named, the filter you listed should work just fine. I think it's more likely that the metadata is missing.

Umm... Also try running pvscan -d to get more debugging data.

Best Answer

Related Solutions

DRBD – Experimenting with DRBD and Virtualization

Lvm – DRBD LVM – backed vs. physical & LVM filter

Related Topic