On 07/19/2010 11:04 AM, Konstantin Svist wrote:

Just noticed that I got this in /var/log/messages when I sized it down:
Jul 18 12:00:44 slon kernel: md0: detected capacity change from 
900199022592 to 300066275328
Jul 18 12:00:44 slon kernel: md0: unknown partition table

And scraped from command line session:

[root@slon ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[3] sda4[0] sdc1[2] sdb1[1]
      879100608 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
[root@slon ~]# mdadm --grow -z 293033472 
--backup-file=/root/grow_md0_size.bak /dev/md0
mdadm: component size of /dev/md0 has been set to 293033472K
[root@slon ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[3] sda4[0] sdc1[2] sdb1[1]
      293033472 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]

Looks like instead of setting the number of blocks per-drive (as per 
the man page), the -z option set the number of total blocks for the 
array, instead. Which means I'm very thoroughly screwed.

Right now I'm trying to reshape back to the old chunk size and will 
then try to resize the array back to the previous size. If the chunk 
size change and array resize are both fully reversible -- and I don't 
think I'm THAT lucky -- then I might be able to get some stuff back.
Will see, I guess.

Can someone confirm that this command should work to revert the size?
mdadm --grow -z 879100608 --backup-file=/root/grow_md0_size_revert.bak 
/dev/md0