[CentOS] Re: Building software RAID mdmad adding a second disk

Thu Apr 13 13:29:32 UTC 2006
israel.garcia at cimex.com.cu <israel.garcia at cimex.com.cu>

Thanks Alexandar for your soon answer, BUT, is there another easier way
to do this?


>>Quoting israel.garcia at cimex.com.cu:

> >>How can I build a RAID 1 of all my particions of sda using mdadm?

>>1. Boot into rescue mode.

>>2. Shrink each file system a bit.  Generally you'll use resize2fs 
>>utility.  MD uses some space at the end of partition for its metadata,

>>and you don't want this to overwrite the end of your filesystem.  Most

>>HOWTOs on the net list this as one of the last steps (after mirrors
>>created).  However if you do this as last step, in rare cases it may 
>>lead to data loss.  You probably want to be on the safe side and
>>file systems first (this will insure your data is secure).  I'm not 
>>sure by how much you need to shrink, should be somewhere in 
>>documentation how many sectors at end of partition MD uses for 

>>3. Create mirror(s) using mdadm.  Create using only one real partition

>>and use "missing" instead of second partition (wish Anaconda installer

>>would allow for something like this).  Then use mdadm to add second 
>>partition to the mirror.  Something like:

>># mdadm --create /dev/md0 --run --level=1 --raid-devices=2 /dev/sda1
>># mdadm /dev/md0 -a /dev/sdb1

>>4. Edit /etc/fstab file.

>>5. You'll need to rebuild initrd image(s) for installed kernel(s).  
>>Just mount your filesystems somewhere, chroot into it and run
>>  Mkinitrd should be smart enough to figure it'll need md device 
>>drivers by looking into fstab file.  Use -v option to mkinitrd to make

>>sure it included needed drivers into new initrd image.

>>6. Configure boot loader (LILO or Grub, whicever you use) to reflect 
>>changes.  Make sure you install boot loader into MBR of both drives.

>>See Ya' later, alligator!