RAID disk failure

[Jeffrey Ross]

On 12/18/2011 12:51 PM, Sam Varshavchik wrote:
> Jeffrey Ross writes:
>
>> It finally happened I had a disk failure in my RAID-1 system, I got a 
>> message from SMART telling me that I had a drive failing and  and 
>> checked the mdstat and sure enough /dev/sda was missing/failed.
>>
>> Ok, drive has been replaced and I did the following:
>>
>> 1) recreated the partition table with "sfdisk -d /dev/sdb | sfdisk 
>> /dev/sda"
>> 2) re-added the partitions back to the raid system (eg mdadm --add 
>> /dev/md1 /dev/sda1  etc...)
>> 3) recreated the boot sector on the new drive  ***WAIT*** ran into an 
>> issue....
>>
>> The system was upgraded (via yum) from 14 to 15 to now 16 so I had 
>> grub, not grub2 on the system, previously it was a simple 
>> "grub-install /dev/sdX"
>>
>> since grub has been replaced with grub2 I tried:
>>
>> # grub2-install /dev/sda
>> /sbin/grub2-setup: warn: Your core.img is unusually large.  It won't 
>> fit in the embedding area..
>> /sbin/grub2-setup: error: embedding is not possible, but this is 
>> required for cross-disk install.
>>
>> so that didin't work, I'm doing something wrong, suggestions?
>
> Carefully review the existing partition layout on what I presume is 
> your good disk, /dev/sdb, and compare it with your recreated partition 
> table on /dev/sda.
>
> Hopefully, on /dev/sdb, your first partition starts on sector 2048, 
> and not sector 63. You probably partitioned your new /dev/sda with the 
> first partition starting on sector 63, which does not leave enough 
> room to install grub. You'll have to start over. Fail and drop all 
> your sda partitions on of all your md arrays. Create a new partition 
> table on sda, recreating the partitions exactly how they are on sdb, 
> starting with sector 2048, matching the start and the end of each 
> partition, on sda, exactly how they exist on sdb. Then you'll be able 
> to install grub.
>
> If your sdb partitions start on sector 63, and you have no room to fit 
> them on sda starting at sector 2048, you'll have to recreate all but 
> your smallest partition on sda, then add and sync them to your array.
>
> For the smallest partition, create it on sda making it as big as it 
> can be. Create a new md array for it on sda, with just one unit. I 
> believe you should be able to format it and mount it, even though its 
> degraded. Then you can manually copy over the contents from sdb, then 
> drop the array on sdb, and add its partition to the replacement md 
> array on sda.
>
>
>
    Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *          63      787184      393561   fd  Linux raid 
autodetect
/dev/sdb2          787185    16418429     7815622+  fd  Linux raid 
autodetect
/dev/sdb3        16418430    24418799     4000185   fd  Linux raid 
autodetect
/dev/sdb4        24418800  1953520064   964550632+   5  Extended
/dev/sdb5        24418863    40050044     7815591   fd  Linux raid 
autodetect
/dev/sdb6        40050108    55665224     7807558+  fd  Linux raid 
autodetect
/dev/sdb7        55665288  1953520064   948927388+  fd  Linux raid 
autodetect

Bingo, mine start at 63, probably a hold over from previous installs.

ok, sdb1 is /boot, and I'm currently using 81 meg out of 372 meg and if 
I'm doing my math right I should be able to easily shrink /boot by 
another 1985 blocks (roughly 1MB) or so.

Based upon what you've given me, I suspect I can simply fail /dev/md1 
(sda1 sdb1) resize it on the sda1 disk, copy everything across via cpio, 
install the new bootloader on /dev/sda, once it comes up I can then 
resize /dev/sdb1 re-add the partition to RAID and run the grub2-install 
command.

Thanks,
Jeff



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