Expanding existing RAID-5 with 2 disks simultaneously or first disk resync and then second?

Hello,

OMV has not the functionality to do this in the GUI.

You have to add the disks manually with mdadm in CLI.

have a look at this post:
Grew RAID5 cant grow filesystem, only spare?

Re,

Zitat von tsch

is expanind an existing RAID5 (4x4TB) with 2 disks faster than expanding with the first disk, resyncing an after resync adding the second disk?

Yes, and safer too ...

Zitat von tsch

I had an issue adding the fourth disk to the RAID-5 having OMV3 adding the disk as spare. How can I avoid this?

It is the default behavior of mdadm if adding a disk, you have to issue the special "grow" parameter later - even on console!
I never tried to mix both commands ...

If you want to add the drive on console too, issue this commando first:
mdadm --add /dev/mdX /dev/sd# (X is a number and # is the letter of the new drive)
(it is absolutely the same while adding it via OMV-WebGUI)

For the growing you have to issue the special grow-command on console - in both ways it is the same command on console:
(When added via OMV-WebGUI / drive is spare:)
mdadm --grow --raid-devices=X /dev/mdY (please change X and Y to your needs!), or
mdadm --grow --size=max /dev/mdX (should also work)

After issuing this commando, the rebuild will start immediately ... and after finish this task, you have to grow your filesystem too (extra command denpending on your used fs). Use:
cat /proc/mdstat to check the ongoing via console ... or the OMV-WebGUI

Sc0rp