Sync Servers with DRBD
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
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.
As it was mentioned already, DRBD isn't greatest solution especially if you have a requirements for further scale. I believe that the best solution on Linux would be Ceph Cluster - https://en.wikipedia.org/wiki/Ceph_(software) with its native cluster aware file system CephFS. For the configuration of an HA storage on Windows, take into account StarWind VSAN Free, which can be deployed in cloud as well (Asure/AWS).
Yes, you can absolutely do that! See:
https://docs.linbit.com/doc/users-guide-83/s-three-nodes/
The only problem you need to have cluster-aware file system or do active-passive-passive mode with file system remount on failover (in this case only one node can have operational write-capable application). Good cover story is here:
https://forums.starwindsoftware.com/viewtopic.php?f=5&t=1392
P.S. DRBD isn't greatest solution we have for HA storage these days, so I'd encourage to take a look at something more OS-specific.