Software RAID with mdadm
From MyWiki
I had a RedHat server that I managed to screw up, while testing different things, to the extent that an re-built was in order. The machine had no RAID controller and I was using software RAID, but couldn't find previous notes on how did I configure it, hence this page that I put together while rebuilding the system.
The server has 6 146G drives and runs RedHat EL 5.3. OS installed via kickstart and the first two drives used in RAID1. I had the rest 4 to play with. The server is going to be an NFS server with moderate load, so I decided to go with RAID5 in the end, to get more space. But initially I was thinking to build RAID10, so the notes have both set of commands.
First, I partitioned disk 3 for use with md.
fdisk /dev/sdc
Choose p to see if the disk has any partitions and delete it (hope you had backups of all the data). Mine had none, so I moved to creating new partition and changed the ID of the newly created partition to fd (Linux raid auto). Wrote changes and quit fdisk.
Now, I need to do the same on the rest of the drives. You can do it in one go, instead of getting into fdisk every time:
for d in d e f ; do sfdisk -d /dev/sdc | sfdisk /dev/sd${d} ; done
Check that we have it the way we wanted:
fdisk -ul /dev/sd{c,d,e,f}
Disk /dev/sdc: 146.8 GB, 146814976000 bytes
255 heads, 63 sectors/track, 17849 cylinders, total 286748000 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sdc1 63 286744184 143372061 fd Linux raid autodetect
Disk /dev/sdd: 146.8 GB, 146814976000 bytes
255 heads, 63 sectors/track, 17849 cylinders, total 286748000 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sdd1 63 286744184 143372061 fd Linux raid autodetect
Disk /dev/sde: 146.8 GB, 146814976000 bytes
255 heads, 63 sectors/track, 17849 cylinders, total 286748000 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sde1 63 286744184 143372061 fd Linux raid autodetect
Disk /dev/sdf: 146.8 GB, 146814976000 bytes
255 heads, 63 sectors/track, 17849 cylinders, total 286748000 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sdf1 63 286744184 143372061 fd Linux raid autodetect
Time to create the RAID. For RAID10 you do this:
# mdadm --create /dev/md3 --level 10 --raid-devices=4 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1
mdadm: /dev/sdc1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Thu Dec 4 15:15:03 2008
mdadm: /dev/sdd1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Thu Dec 4 15:15:03 2008
mdadm: /dev/sde1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Thu Dec 4 15:15:03 2008
mdadm: /dev/sdf1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Thu Dec 4 15:15:03 2008
Continue creating array? y
mdadm: array /dev/md3 started.
Check that it's building:
# cat /proc/mdstat
Personalities : [raid1] [raid10]
md3 : active raid10 sdf1[3] sde1[2] sdd1[1] sdc1[0]
286743936 blocks 64K chunks 2 near-copies [4/4] [UUUU]
[>....................] resync = 0.3% (1005312/286743936) finish=89.9min speed=52911K/sec
md0 : active raid1 sdb1[1] sda1[0]
128384 blocks [2/2] [UU]
md1 : active raid1 sdb2[1] sda2[0]
1052160 blocks [2/2] [UU]
md2 : active raid1 sdb3[1] sda3[0]
142191232 blocks [2/2] [UU]
unused devices: <none>
Now, I created physical volume to use with LVM:
# pvcreate -ff /dev/md3 Really INITIALIZE physical volume "/dev/md3" of volume group "datavg" [y/n]? y WARNING: Forcing physical volume creation on /dev/md3 of volume group "datavg" Physical volume "/dev/md3" successfully created
And created volume group:
# vgcreate datavg /dev/md3 Volume group "datavg" successfully created
To do RAID5, you would need this commands:
# mdadm --misc --stop /dev/md3 # mdadm --create /dev/md3 --level 5 --raid-devices=4 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1
I stopped the freshly built RAID10 and created RAID5 instead. If you're doing it with no existing RAID devices, you can skip stop command.
