I have 4 disks in my server. sda and sdb were combined to RAID1 and had the operating system. sdc and sdd were a second RAID1 device that had a single volume group with a bunch of LVMs. sdd died so my data RAID got degraded. After replacing sdd (but before adding to the RAID), grub decided lose it's mind and refuse to boot. The fastest way to fix was to just reinstall the OS since there was nothing important on it.
I removed sdc and sdd during the install to make sure they were not overwritten by mistake. After the install was finished, I put the drives back in, and Centos found my volume group automatically. sdc was no longer part of a RAID array though.
It is partitioned /dev/sdc1 Linux raid auto detect
My question is - how can I use mdadm to recreate the sdc1,sdd1 RAID array without losing data already on sdc?
My best guess was to create the array with just sdc1 first, then add sdd1 after (so it rebuilds from sdc to sdd)
EDIT After looking at the output of /cat/mdstat again, I noticed something odd. My data disk was showing up as part of a RAID array, but one of my OS RAID arrays was missing (and fstab tried to link my swap to my data disk).
fdisk /dev/sda Device Boot Start End Blocks Id System /dev/sda1 * 1 32 257008+ fd Linux raid autodetect /dev/sda2 33 2072 16386300 fd Linux raid autodetect /dev/sda3 2073 30401 227552692+ fd Linux raid autodetect
md1 should have been /dev/sda2 and /dev/sdb2 however it is missing
cat /proc/mdstat Personalities : [raid1] md2 : active raid1 sdb1 sda1 256896 blocks [2/2] [UU] md3 : active raid1 sdc1 1465135936 blocks [2/1] [U_] md0 : active raid1 sdb3 sda3 227552576 blocks [2/2] [UU]
When I try to create md2, I get:
[root@xen2 ~]# mdadm --create /dev/md1 --level=1 --raid-disks=2 /dev/sda2 /dev/sdb2 mdadm: /dev/sda2 appears to be part of a raid array: level=raid1 devices=2 ctime=Wed Aug 15 02:48:06 2012 mdadm: /dev/sdb2 appears to be part of a raid array: level=raid1 devices=2 ctime=Wed Aug 15 02:48:06 2012 Continue creating array? n
mdadm scan also shows it missing
[root@xen2 ~]# mdadm --detail --scan ARRAY /dev/md0 level=raid1 num-devices=2 metadata=0.90 UUID=51ef54bd:770bb58e:90183df1:d82a79c7 ARRAY /dev/md3 level=raid1 num-devices=2 metadata=0.90 UUID=2d7dfb1e:6b091396:a7558ec2:4d288e6f ARRAY /dev/md2 level=raid1 num-devices=2 metadata=0.90 UUID=ecdd769b:c49d51b6:fe43f166:465b7073
I'm not sure why /dev/md1 decided to get lost after rebooting, but is it safe to rebuild the it?