[olug] Software RAID / accidentally raidhotadd to wrong md

[lug at robotz.com]

Issue summary:  Had problems with 1 of a 3 drive software raid array.
Harddrive is not physically bad, but the array failed today on boot.
Used “raidhotadd” to get all of the raid5 partitions (md0 – md3) 
up and running with the exception of the most important partition 
(md4).

I accidentally tried to “raidhotadd” 2 of the 3 drives from md4 into 
md2.  Now hdb2 and hdc2 think they are part of md2 when they actually 
should be part of md4.  This is not reflected in /etc/raidtab but 
must be stored somewhere I cannot find. (superblock?)

This leaves only 1 drive in md4 and therefore md4 will not start 
even degraded.  md4 is a RAID 5 partition, which is supposed to include 
hda2, hdb2, and hdc2.  Since RAID wont start on md4, I cannot simply 
use “raidhotremove” and “raidhotadd” to correct this mistake (assuming 
that would correct the mistake).

I used “raidsetfaulty” to deactivate hdb2 to stop interfering with 
the start of md2.  (because hdb2 belongs in md4 and raidhotremove 
refuses to get hdb2 out of md2 without deactivating the partition)

lsraid reports md0 – md3 correctly.  However, typing “lsraid –A –d 
/dev/hdb2” or “lsraid –A –d /dev/hdc2” shows them as a member of 
md2 still.  They should be in md4 instead.

My question #1:  Did my mistake hose the data in both hdb2 and hdc2 
making it impossible to recover md4 (my most critical partition containing 
/home) or is hdb2 and hdc2 merely confused about where they belong 
but still within them is my critical data making recovery of md4 
possible?

My question #2: If recovery is possible, should I then “mkraid /dev/md4 
–f” and hope for the best or is there a safer way to _save_ my data? 
Or perhaps there is a way to make hdb2 and hdc2 realize again that 
they are part of md4.   

Keep in mind that since md4 won’t start I can’t reverse the mistake 
with raidhotadd.

If I failed to provide any details please let me know and I will 
elaborate further.

Thank you.