Hi,
Just if anyone is curious, I thought I'd share my latest success story with OMV.
Long story short: My NAS initially had a RAID 5 with 3x16TB Seagate Exos X16 (32TB usable) MDADM Ext4, and I've upgraded it to 4x16TB flawlessly. That said, it was a week long of a bit stressful tasks to process.
I'm using OMV for backuping my datacenter dedicated servers, and for production work.
I'm lucky enough to have a great internet, with 8Gbit/s download and 2Gbit/s upload speeds, and I've equipped my home/office network with full 10Gbit/s, which allows for fast, comfortable and interesting uses.
I love it!
Most critical data is on my PCs (desktop and laptop) which is synced to my off-site web server's Nextcloud, which itself is backed-up on the NAS on a nightly basis.
For the rest, I don't currently have an off-site or offline backup of this NAS as it is logistically pretty expensive and complex to put out.
Over the years of using OMV (since 2017), I had to replace 2 failing drives. One around 2018, and one around 2022 I think (just after upgrading to the Exos array, one drive died like 2 weeks after creation, as failures usually happen pretty quickly when a drive will fail).
Recently, one drive started to softly fail due to oldness this time (SMART error, invalid sector, warning sent by mail by OMV, as I enabled SMART monitoring).
This time I wouldn't take risks as the NAS is now holding important data.
So I bought a replacement disk, then did the RAID rebuild and sent the failing one to RMA.
Rebuild went flawlessly, took around 24h, just like first initialization, during which the NAS was obviously slower than usual.
Once the replacement drive came up, I was surprised to see it was a 16TB Exos X18. Fortunately, this equal or better than the X16 so it is fully compatible with my RAID array. Then I thought: Why not extend the RAID?
So I've proceeded to renting a new temporary server at Hetzner in order to backup all important data.
This took almost 3 days to backup at near 1Gbit/s speed.
Here is the NAS activity during this time (Download at the beginning is unrelated).
I should have done this before and should keep this server. But the plan is to add an OMV NAS at family's house with daily backup from my NAS. Over time this will be far less expensive.
Once the backup was done, I've used OMV's Grow feature.
To do so, I shut down the NAS as this is a classic PC case, then added the drive.
After rebooting, within OMV, went to Storage > Multiple Devices > Grow.
Then I selected the device, validated. Weird thing is it started the MDADM process (visible with 'cat /proc/mdstat') , but it still asked me to apply changes, which I did.
Grow process is far slower with intense write/reads during the first 2/3 of the process. Then, for the 33% remaining, it is as fast as a rebuild.
Overall, took around 2.5 days.
Once done, I shut down the NAS, and booted on a GParted live via USB stick.
Interestingly, GParted asked to check the device instead of grow as I would have thought. So I did that.
After an initial check, it did the resize2fs by itself.
This whole GParted process took around 1 hour. Most stressful part as I was really into the unknown at this point.
Once done, rebooted to OMV, and everything worked flawlessly with now 48TB (43.4TiB) available.
Hope this is useful to anyone wanting to do the same.
If you proceed to this, don't forget to backup as if one single drive fails during the grow process, I would assume you'd lose the array.
Anyway, I wanted to tell my deep thanks to the OMV team, as your tools helps me doing my personal as well as professional stuff on a daily basis, free of any limitation, thanks to Debian (rather than a limited proprietary all-in-one solution).
Thank you all 