Comments on: Recovering a RAID5 mdadm array with two failed devices

By: RAID5 degradado y sin superbloque md en una de las unidades restantes

RAID5 degradado y sin superbloque md en una de las unidades restantes — Fri, 29 Mar 2019 02:35:53 +0000

[…] A continuación lea este blog bastante largo en http://blog.al4.co.nz/2011/03/recovering-a-raid5-mdadm-array-with-two-failed-devices/. […]

By: ediaz_ultreia

ediaz_ultreia — Thu, 21 Dec 2017 16:26:54 +0000

Thanks for your post. I had to resucitate an old machine decomisioned long time ago, and this post helped a lot.

By: Alex

Alex — Fri, 26 Sep 2014 17:37:28 +0000

In reply to Daniel Franklin. Glad to hear it!

By: Daniel Franklin

Daniel Franklin — Fri, 26 Sep 2014 16:57:57 +0000

Your instructions saved my data. Thank you. I learned something valuable about RAID5 today :-)

By: Alex

Alex — Fri, 24 Jan 2014 17:47:11 +0000

In reply to Boudewijn Charite. Glad you got your data back. Mdadm can absolutely send email alerts, but you have to configure the address, and have a working MTA.

By: Boudewijn Charite

Boudewijn Charite — Fri, 24 Jan 2014 16:08:24 +0000

I tried the following

mdadm –verbose –create /dev/md1 –chunk=64 –metadate=0.90 –level=5 –raid-devices=4 missing /dev/sdb6 /dev/sdc6 /dev/sdc6

which seemed to work

Then I repaired the file system with fsck.ext4 -cDfty -C 0 /dev/md1

Checked if the data was recovered and i was, than I added the missing drive with

mdadm -a /dev/md1 /dev/sda6

which lead to a rebuild of the array and a booting and working server and all my data is back.

Is it possible that mdadm sent a message when something happens to the array or do I have to move to a hardware aray. A RocketRAID 2720SGL cost around E.180,– so that is not so expansive as it used to be.

By: Alex

Alex — Tue, 21 Jan 2014 19:31:22 +0000

In reply to Boudewijn Charite. One thing I just noticed; your /dev/md1 says chunk size is 512K but your drives say 64K. I can only guess as to how this happened, but make sure you use whatever the array was originally created as. Figuring out the default for your version of mdadm might help with this.

By: Alex

Alex — Tue, 21 Jan 2014 19:19:54 +0000

In reply to Boudewijn Charite.

In the article above I used:
# mdadm –verbose –create /dev/md1 –chunk=512 –level=5 –raid-devices=4 /dev/sdb1 missing /dev/sdd1 /dev/sde1

You’ll need to adapt this for your own scenario, it looks like /dev/sda6 failed first so I’d suggest creating it with that one missing.

By: Boudewijn Charite

Boudewijn Charite — Tue, 21 Jan 2014 19:00:20 +0000

In reply to Alex.

Thanks for you replay Alex

It seem that I lost a drive in december 2012 but did not know that and lost a second one last weekend. This one I noticed because the data was partly accessible. I did shut down the server and discontected alle the hdd and connect them again and all 4 were seen by the bios and the md0 worked again because it booted in safe mode. So I have good hope that most of my data is still fine if I make the right rebuild.

Now I have to know what the right rebuild could / should be.

By: Alex

Alex — Tue, 21 Jan 2014 18:07:28 +0000

In reply to Boudewijn Charite. It's been a while since I've worked with mdadm, so I'm not the best person to get advice from, but it looks like you're trying to create a new array with all the devices of the old one present. The article above describes how to create a new array with only the drive that failed first missing, which should result in a readable array if your data hasn't been corrupted somehow.