software RAID data recovery on Rocks Cluster
We have a software RAID 1 array, and one of the disks (sda) has failed, and a few hundred gigs of data have disappeared. The type is a software not a hardware RAID. Unfortunately, we may not have the resources to get a replacement disk.
-Priority1: Our priority is to recover the data. It contains the research of a few people. What is a good way to access the data safely?
Is it possible to use the following strategy to gain access to the data, then back it up onto an external disk?:
mount /dev/sdb /compute
mount /dev/sda /compute-other
The drive that we have been working on (composed of the RAID1 system) is called /compute. Would mounting the good drive on /compute allow us to gain access to the data and back it up?
-Priority2: Also, to get our system back up and running, without destroying our data, our hope is that we can restore the RAID using the current (failed or kicked out, I am not sure which) sda disk. It has been suggested to me to do this in our system:
mount /dev/md0 /compute
mdadm /dev/md0 --add /dev/sda
but online, I have also seen:
raidhotadd /dev/mdX /dev/sdX
Unfortunately, my knowledge is quite rudimentary and I am not sure which of these options to use, or what is necessary to be able to use them correctly. For instance, do I need to put the system into recovery mode or something? Or run
/sbin/mdadm --assemble --scan
as I have also seen suggested?
A preliminary test suggests to me that we do not have raidhotadd, but we do have the mdadm program.
Any help would be highly appreciated. Thank you.
(more info, FYI, if useful:
system info: CentOS release 4.4 (final) operating system
distribution is Rocks release 4.2.1 (Cydonia)
see attached text file for the contents of /proc/mdstat /etc/fstab and /var/log/messages )