A Beginner's Guide To LVM - Page 8
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8 Replacing The Hard Disks With Bigger Ones
We are currently using four hard disks with a size of 25GB each (at least we are acting like that). Now let's assume this isn't enough anymore, and we need more space in our RAID setup. Therefore we will replace our 25GB hard disks with 80GB hard disks (in fact we will still use the current hard disks, but use their full capacity now - in the real life you would replace your old, small hard disks with new, bigger ones).
The procedure is as follows: first we remove /dev/sdb and /dev/sdd from the RAID arrays, replace them with bigger hard disks, put them back into the RAID arrays, and then we do the same again with /dev/sdc and /dev/sde.
First we mark /dev/sdb1 as failed:
mdadm --manage /dev/md0 --fail /dev/sdb1
server1:~# mdadm --manage /dev/md0 --fail /dev/sdb1
mdadm: set /dev/sdb1 faulty in /dev/md0
The output of
cat /proc/mdstat
looks now like this:
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdc1[0] sdb1[2](F)
24418688 blocks [2/1] [U_]
md1 : active raid1 sde1[0] sdd1[1]
24418688 blocks [2/2] [UU]
unused devices: <none>
Then we remove /dev/sdb1 from the RAID array /dev/md0:
mdadm --manage /dev/md0 --remove /dev/sdb1
server1:~# mdadm --manage /dev/md0 --remove /dev/sdb1
mdadm: hot removed /dev/sdb1
cat /proc/mdstat
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdc1[0]
24418688 blocks [2/1] [U_]
md1 : active raid1 sde1[0] sdd1[1]
24418688 blocks [2/2] [UU]
unused devices: <none>
Now we do the same with /dev/sdd1:
mdadm --manage /dev/md1 --fail /dev/sdd1
server1:~# mdadm --manage /dev/md1 --fail /dev/sdd1
mdadm: set /dev/sdd1 faulty in /dev/md1
cat /proc/mdstat
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdc1[0]
24418688 blocks [2/1] [U_]
md1 : active raid1 sde1[0] sdd1[2](F)
24418688 blocks [2/1] [U_]
unused devices: <none>
mdadm --manage /dev/md1 --remove /dev/sdd1
server1:~# mdadm --manage /dev/md1 --remove /dev/sdd1
mdadm: hot removed /dev/sdd1
cat /proc/mdstat
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdc1[0]
24418688 blocks [2/1] [U_]
md1 : active raid1 sde1[0]
24418688 blocks [2/1] [U_]
unused devices: <none>
On a real system you would now shut it down, pull out the 25GB /dev/sdb and /dev/sdd and replace them with 80GB ones. As I said before, we don't have to do this because all hard disks already have a capacity of 80GB.
Next we must format /dev/sdb and /dev/sdd. We must create a /dev/sdb1 resp. /dev/sdd1 partition, type fd (Linux RAID autodetect), size 25GB (the same settings as on the old hard disks), and a /dev/sdb2 resp. /dev/sdd2 partition, type fd, that cover the rest of the hard disks. As /dev/sdb1 and /dev/sdd1 are still present on our hard disks, we only have to create /dev/sdb2 and /dev/sdd2 in this special example.
fdisk /dev/sdb
server1:~# fdisk /dev/sdb
The number of cylinders for this disk is set to 10443.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): <-- p
Disk /dev/sdb: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 3040 24418768+ fd Linux raid autodetect
Command (m for help): <-- n
Command action
e extended
p primary partition (1-4)
<-- p
Partition number (1-4): <-- 2
First cylinder (3041-10443, default 3041): <-- <ENTER>
Using default value 3041
Last cylinder or +size or +sizeM or +sizeK (3041-10443, default 10443): <-- <ENTER>
Using default value 10443
Command (m for help): <-- t
Partition number (1-4): <-- 2
Hex code (type L to list codes): <-- fd
Changed system type of partition 2 to fd (Linux raid autodetect)
Command (m for help): <-- w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Do the same for /dev/sdd:
fdisk /dev/sdd
The output of
fdisk -l
looks now like this:
server1:~# fdisk -l
Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 18 144553+ 83 Linux
/dev/sda2 19 2450 19535040 83 Linux
/dev/sda4 2451 2610 1285200 82 Linux swap / Solaris
Disk /dev/sdb: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 3040 24418768+ fd Linux raid autodetect
/dev/sdb2 3041 10443 59464597+ fd Linux raid autodetect
Disk /dev/sdc: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdc1 1 3040 24418768+ fd Linux raid autodetect
Disk /dev/sdd: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdd1 1 3040 24418768+ fd Linux raid autodetect
/dev/sdd2 3041 10443 59464597+ fd Linux raid autodetect
Disk /dev/sde: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sde1 1 3040 24418768+ fd Linux raid autodetect
Disk /dev/sdf: 85.8 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdf1 1 3040 24418768+ 8e Linux LVM
Disk /dev/md1: 25.0 GB, 25004736512 bytes
2 heads, 4 sectors/track, 6104672 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk /dev/md1 doesn't contain a valid partition table
Disk /dev/md0: 25.0 GB, 25004736512 bytes
2 heads, 4 sectors/track, 6104672 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk /dev/md0 doesn't contain a valid partition table
Now we add /dev/sdb1 to /dev/md0 again and /dev/sdd1 to /dev/md1:
mdadm --manage /dev/md0 --add /dev/sdb1
server1:~# mdadm --manage /dev/md0 --add /dev/sdb1
mdadm: re-added /dev/sdb1
mdadm --manage /dev/md1 --add /dev/sdd1
server1:~# mdadm --manage /dev/md1 --add /dev/sdd1
mdadm: re-added /dev/sdd1
Now the contents of both RAID arrays will be synchronized. We must wait until this is finished before we can go on. We can check the status of the synchronization with
cat /proc/mdstat
The output looks like this during synchronization:
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdb1[1] sdc1[0]
24418688 blocks [2/1] [U_]
[=>...................] recovery = 9.9% (2423168/24418688) finish=2.8min speed=127535K/sec
md1 : active raid1 sdd1[1] sde1[0]
24418688 blocks [2/1] [U_]
[=>...................] recovery = 6.4% (1572096/24418688) finish=1.9min speed=196512K/sec
unused devices: <none>
and like this when it's finished:
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]
md0 : active raid1 sdb1[1] sdc1[0]
24418688 blocks [2/2] [UU]
md1 : active raid1 sdd1[1] sde1[0]
24418688 blocks [2/2] [UU]
unused devices: <none>
