Is the RAID expandable?

[cirion]

I just changed my Motherboard in the core to one with more sata ports I had lying around...
I can confirm that the software raid still works after changing motherboard even with differen type of sata controller.

I reinstalled LinuxMCE and it found the RADI without my help

Now that I have more ports, I have added a fourth drive and was hoping to expand it from 3xRaid5 to 4xRaid5. Is it possible?

Anyone have any more info on how the raid in LinuxMCE works and what package is used?

[Venom986]

my understanding is that its not possible (or at least not painless) as in a 3-drive RAID5 you have data split 50/50 between two drives and parity on the 3rd.  Moving to a 4-drive RAID5 would require data split 33/33/33 and the 4th drive as parity.

I could be wrong.

[cirion]

I hope you are wrong

I have found this about software RAID in Ubuntu:
http://ubuntuforums.org/showthread.php?t=408461

And this about a utility to manage software RAID in linux:
http://www.linuxmanpages.com/man8/mdadm.8.php

I also have a Thecus n5200, that uses software RAID in linux, and it is able to expand all the way from a 2 disk RAID1-> 3-5 disk RAID5. That way I was able to expand the RAID with a disk when needed. I both suspect and hope that the software raid in my Thecus is the same as in LinuxMCE.

[colinjones]

Actually, venom, its much more complicated than that! On a RAID5 array both data and parity are on all disks in the array (striped). There is no "parity" disk. If you want that you are looking for RAID 3 or 4. But they perform even worse than a RAID5 which is pretty bad in itself!

[Venom986]

http://www.mythtv.org/wiki/index.php/LVM_on_RAID

Dependant on kernel support, but nice and promising   Of course, all 6 of my SATA ports are used already...but its nice to know anyways.

[cirion]

I jumped...

I just added the drive as a spare in the Webadmin then ran the following command:

Code Select Expand

linuxmce@dcerouter:~$ sudo mdadm --grow /dev/md1 --raid-disks=4
mdadm: Need to backup 384K of critical section..
mdadm: ... critical section passed.
linuxmce@dcerouter:~$


Webadmin now tells me:
DAMAGED, REBUILDING (0/100)

Should take a day to rebuild... I will post more when I know what the end result is...

[cirion]

Still rebuilding... 0/100 still... After 1 hour.
The data on the RAID is still available

Better leave it alone to rebuild for now...

[jondecker76]

Please keep us informed - this is information that I would really like to know for sure!

[cirion]

I will keep you informed....

2.5 hours rebuilding now. Status is still damaged and the disks are still working hard.
What has changed, is the type of the disk in the Webadmin. It's no longer marked as a spare, but a active disk
The Capacity is marked differently than the others, that might change when its done...

ID   Drive              Capacity              Type           Status
35   /dev/sda   750.1 GB, 0x0000000 GB   active disk   OK   
36   /dev/sdb   750.1 GB, 0x0000000 GB   active disk   OK   
37   /dev/sdc   750.1 GB, 0x0000000 GB   active disk   OK   
39   /dev/sdd   750.1 GB              active disk   OK

[cirion]

3.5 hours... Status is now:
DAMAGED, REBUILDING (20/100)

[cirion]

5.5 hours... Status is now:
DAMAGED, REBUILDING (20/100)

[cirion]

9.5 hours... Status is now:
DAMAGED, REBUILDING (60/100)

[jondecker76]

sure looks like its going to work!

[cirion]

I shure hope so... But it could still end in tears... I don't have backup of all the files... But at least I have all important stuff.

11.5 hours... Status is now:
DAMAGED, REBUILDING (80/100)

[cirion]

13 hours... It was 1395GiB Now it is:

34   CORE   Software Raid 5   Software Raid 5   /dev/md1   4   2093.08GiB   OK

Going to bed, I'll test the raid tomorrow.. Looks like all the data is there