Will this RAID survive an Ubuntu installation?

September 8, 2012 11:43 AM

I have an Ubuntu installation with a software RAID. The Ubuntu installation is on a separate disk than the RAID. If I reinstall Ubuntu, will it find and mount the RAID successfully?

My gut says yes, but I wanted to check...

posted by geoff. to Computers & Internet (5 answers total)

I'm not sure. I had to repair my Ubuntu installation after a power failure, and it decided it wasn't on a RAID 1 array any more, even though the installation was on a disk in the array. I manually recreated the array and, after re-syncing the second disk, everything went back to normal.

So I'm not sure if it's going recognise the array automatically, but it ought to be straightforward to rebuild it without any data loss if it doesn't.
posted by pipeski at 12:03 PM on September 8, 2012

Best answer: Your RAID will definitely survive, but I don't know if it will be auto-detected it. If it's LVM (aka "device mapper") RAID, in my experience it should just work. If it's an "md" RAID, then you might have to save your mdadm.conf file, but even if you don't you can still run a command to detect the RAID manually. I think it's something like "mdadm --scan --reassemble", in case you need it, but check the man page to be sure.
posted by vasi at 12:05 PM on September 8, 2012

Desktop version of the ubuntu installer? I'm not sure what will happen there, but as i recall the disk config section of the curses-driven alternative editor does a pretty good job of rediscovering md arrays.
posted by Good Brain at 12:56 PM on September 8, 2012

I've had very positive experiences dealing with md arrays, but I keep my mdadm.conf floating around in a few alternative places along with notes about which drive is plugged in where (so /dev/sda is /dev/sda and /dev/sdb is /dev/sdb, etc.) because I'm paranoid that one day I'll unplug something or swap something and screw something up. But my 12 TB array has been churning away for almost two years now without a single issue, so my paranoia so far has been for nothing.

TL;DR: You should be fine, make note of which device is what and grab your mdadm.conf if you can.
posted by Brian Puccio at 3:08 PM on September 8, 2012

I don't know about the desktop/GUI installer, but d-i (aka "debian-installer", the installer on the alternate install cd) will detect the md device and present the RAID volume and any LVM inside that during the partitioning stage.

d-i will let you get to the partitioner before anything gets written to disk, so you can boot and run the installer and confirm everything is detected correctly without damaging your existing install.

(include "installers are dangerous if you make a mistake, make sure you have a current backup of all data you care about before starting" disclaimer here)
posted by russm at 4:17 AM on September 9, 2012