I have 4 disks in a RAID5 array. I want to add a 5th. So I did mdadm --add /dev/md3 /dev/sde1 This worked but, as expected, the disk isn't being used in the raid5 array.
md3 : active raid5 sde1[4] sdd4[3] sdc3[2] sdb2[1] sda1[0] 2930279808 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
So then I tried the next step: mdadm --grow --raid-devices=5 /dev/md3
But now I have problems... mdadm: Cannot set device size/shape for /dev/md3: Invalid argument
Can CentOS 4.6 grow md5 arrays? Or is the kernel and mdadm version too old?
( http://www.economysizegeek.com/2006/07/15/migrate-raid1-to-raid5-and-grow/ hints that I need 2.6.17 and mdadm 2.5.2, but it's hard to know what the RHEL/CentOS kernel has in it 'cos version numbers no longer match)
I wonder if I could boot off a Ubuntu CD or something and grow the array that way. Would be annoying (many hours of server downtime)...