software raid with pending failure

[Aaron Bliss]

Hi everyone,
I'm running redhat es 5 with several raid 1 partitions setup.  It looks like /dev/sdb is getting ready to fail.  I noticed the following in the logwatch report:

/dev/sdb - 29 Time(s)
  1 offline uncorrectable sectors detected 

So, in order to correct the pending failed drive, I marked each /dev/sdbx partition that was partitioning in a raid1 as failed with mdadm, and then removed the dev/sdbx with madam.  So I was running the os from /dev/sda only.  So far so good.  

I then took the box down and unplugged the device that I believed was /dev/sdb, however the box wouldn't boot.  It just sat at the grub prompt.  So, I thought, maybe the box is seeing the other drive as /dev/sdb.  So, I turned the box back off, plugged in the previous drive, unplugged the other drive, and the box wouldn't boot.  I got to the grub splash screen, however the box just kept resetting itself.  So, I plugged that drive back in, and the box booted up fine.  So, I'm now working with what I believe to be a good drive and a soon to be failed drive.  So, a few questions here.  1. How do I identify which hard drive is /dev/sda and which is /dev/sdb?  2. Why wasn't I able to boot with a single drive (assuming that at least 1 of them is good)?  3. How do I go about replacing the bad drive?  Thanks for your help.  Below is a print out of /dev/mdstat before failing and removing /dev/sdb from the mirrors (all raid partitions were setup during the install of the operating syst
 em)

md0 : active raid1 sdb1[1] sda1[0]
      513984 blocks [2/2] [UU]

md5 : active raid1 sdb2[1] sda2[0]
      204796544 blocks [2/2] [UU]

md1 : active raid1 sdb5[1] sda5[0]
      3068288 blocks [2/2] [UU]

md4 : active raid1 sdb6[1] sda6[0]
      2048192 blocks [2/2] [UU]

md3 : active raid1 sdb7[1] sda7[0]
      2048192 blocks [2/2] [UU]

md2 : active raid1 sdb3[1] sda3[0]
      10241344 blocks [2/2] [UU]

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/md2              9.5G  2.2G  6.9G  24% /
/dev/md0              487M   19M  443M   5% /boot
tmpfs                 755M     0  755M   0% /dev/shm
/dev/md5              190G  1.4G  179G   1% /opt/zimbra
/dev/md3              1.9G   81M  1.8G   5% /tmp
/dev/md4              1.9G  152M  1.7G   9% /var  

-- 
Aaron Bliss
Systems Administrator
SUNY Brockport
(585) 395-2417