Fixing a Linux RAID 1 software mirror

[Christopher K. Johnson]

Christopher K. Johnson wrote:

> Michael Mansour wrote:
>
>> Hi,
>>
>> I've just noticed I have the following issue on my
>> /home (/dev/md5) software RAID mirror:
>>
>> [root at gazelle root]# lsraid -a /dev/md5
>> [dev   9,   5] /dev/md5        6A995494.6BAA9433.BC09B08A.778BCE84 
>> online
>> [dev   ?,   ?] (unknown)       00000000.00000000.00000000.00000000 
>> missing
>> [dev  34,   8] /dev/hdg8       6A995494.6BAA9433.BC09B08A.778BCE84 good
>>
>> With the raidtab showing:
>>
>> raiddev             /dev/md5
>> raid-level                  1
>> nr-raid-disks               2
>> chunk-size                  64
>> persistent-superblock       1
>> nr-spare-disks              0
>>    device          /dev/hde8
>>    raid-disk     0
>>    device          /dev/hdg8
>>    raid-disk     1
>>
>> and the /proc/mdstat shows:
>>
>> md5 : active raid1 hdg8[1]
>>      20972736 blocks [2/1] [_U]
>>
>> As /dev/md5 is my /home directory, I don't want to
>> lose any data. How can I fix this to get /dev/hde8
>> into the md5 raidset without losing my data?
>>  
>>
> I would check whether /var/log/messages shows why you lost that 
> mirror. And if the device is responsive at all you might want to run 
> some diagnostics on that hard drive /dev/hde using smartctl.

In case you don't have it yet, smartctl is part of the kernel-utils package.

>
> Also you will want the mdadm package installed if it isn't already. 
> Configure an email address in /etc/mdadm.conf on the MAILADDR line 
> that will reach you. Then:
> chkconfig mdmonitor on
> service mdmonitor start
> That way you will be notified whenever there is a raid failure event 
> in the future.
>
> The missing and (unknown) indication I have seen once, and it was when 
> a hard drive failed completely. In my case the hard drive had to be 
> replaced, but some of the scsi controller status was wedged due to the 
> unresponsive drive. So I was not able to hot-swap the drive as the 
> same drive name. I ended up having to shutdown, swap drives, and boot 
> back up, then partition the new drive and bring mirrors in sync.
>
> Is hde partitioned the same as hdg? If so you can do this to partition 
> the new drive:
> sfdisk -d /dev/hdg >parts.hdg
> sfdisk /dev/hde <parts.sdg
>
> Do you have a swap partition on the drive? If so you will need to do a 
> mkswap for that partition and a swapon to bring it online.
> mkswap /dev/hdgN

oops! that would be 'mkswap /dev/hdeN' where N is the swap partition number.

> swapon -a
>
> With mdadm package installed - to resync hde8 (If your disk is 
> actually fine, then this is the only step you need):
> mdadm /dev/md5 -–add /dev/hde8
> [repeat for other raid partitions that need to be sync'd]
> cat /proc/mdstat # to show progress of synchronization
>
> Do you boot from that drive? If so you will need to fix the grub or 
> lilo mbr after synchronization of partitions is completed.
>


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   "Spend less!  Do more!  Go Open Source..." -- Dirigo.net
   Chris Johnson, RHCE #807000448202021