Growing RAID 6 with OMV (MDADM)

wexcide · 10. Juli 2016

Hello fellow OMV'ers!

I currently run an HP MicroServer Gen8 with OMV 2.x on it (SSD boot drive & x4 2TB WD Reds). I have MDADM (OMV's out of the box RAID) setup as a RAID 10. MDADM does not support growing RAID 10 unfortunately which is understandable the way RAID 10 is laid out.

I am about to start building a new storage box, most likely a Supermicro 4U setup (24 3.5 bays). I am going to start it off with x4 4TB HGST Deskstar NAS drives. I do not really need the performance gain from RAID 10, so I am planning on doing a RAID 6 this go around. (I will take the hit of capacity vs reliability to avoid RAID5).

From my understanding MDADM does support growing RAID 6 pools, so my question is does OMV recognize and support growing RAID 6 pools when I add more drives down the line? And if so, what is the risk involved in growing a RAID 6(RAID 5 growing is pretty risky). I keep all my data backed up to Crashplan via the headless client running underneath OMV/on debian, but I would still like to avoid data loss because restoring backups over the cloud like that with my amount of data, even on a 100 fiber line, take forever. ( I will likely make an external local backup of all data when the time comes but still)

If this isn't the best option, could someone recommend a better path to take?

SerErris · 11. Juli 2016

OMV itself does recognize the grown MD size.

Hoever you need to grow your filesystem on it as well. You can do this in OMV section

OMV->Storage->File Systems

If you select the File System you can grow it.

The Risk of the mdadm operation is the same regardless of Raid6/5. Also I do not really see the risk in there. The activity incorporates to recalculate the parity for all data area, to reflect the number of disks in this raid. The only risk might be a complete power loss.

I have not tested it, but afaik the operation of adding is a very short one and then the raid is in degraded mode. So if you do not have a disk failure during the rebuild, you should be fine.

Also a good backup is allways advised for those operations.

Regards
Ser

wexcide · 12. Juli 2016

Thanks for the response! RAID 6 it is! I always keep a backup of my data, at a minimum offsite and usually a local as well.

Orangeday · 24. Juli 2016

May I ask how you plan to transfer your data?
I'm planning to establish a RAID 6 system next week.
The drives are in use in my computer at the moment and I'm wondering how I should transfer them to the NAS.
Could I buy one more drive, put it in the NAS as RAID 0 and empty a drive of my PC on it? Then put the emptied drive in the NAS, change RAID 0 to RAID 5 and transfer the data of another one? And once I have 4 drives in the NAS I change it to RAID 6?
Or is there an easier way?

Sc0rp · 25. Juli 2016

Hi,

i don't think, that is the best way ...

Consider the following strategy:
- build up your NAS box with 2 drives (one system, one data)
- create on the data-drive a "degraded raid1"
- move data
- add the new drive to the raid1 as hotspare (instantly the rebuild starts)
- move the old drive from "computer" to NAS box
- start raid-level-migration from raid1 to raid5

Since i'm more a console freak, i dunno how it works from OMV-WebGui ...

Sc0rp

vl1969 · 25. Juli 2016

Zitat von Sc0rp

Hi,

i don't think, that is the best way ...

Consider the following strategy:
- build up your NAS box with 2 drives (one system, one data)
- create on the data-drive a "degraded raid1"
- move data
- add the new drive to the raid1 as hotspare (instantly the rebuild starts)
- move the old drive from "computer" to NAS box
- start raid-level-migration from raid1 to raid5

Since i'm more a console freak, i dunno how it works from OMV-WebGui ...

Sc0rp

Alles anzeigen

I do not think you can do all this from WebUI.
it has to be via CLI.

also do you really need mdadm RAID setup with all this complexity.?

may be you can consider SnapRaid+mergerfs?
it is not a real time raid setup but works pretty well in OMV and you can setup and manage it all from web UI. except transfer data. that needs to be done in CLI. you can configure sync and scrub jobs as often as you need to get almost real time benefits.
and with snap raid setup you can grow and shrink the pool at will. multiple parity drives (if I remember correctly up to 6), can use drives of different sizes(the only restriction is that parity drive(s) must be the as large or bigger than largest data drive in the pool.)

in my setup I am going with raid-1 only on system drive. it will never grow and I just want to better up-time for the system.

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