Raid:Manual Rebuild
Raid: Manual Rebuild
SME Servers Raid Options are largely automated, if you built your system with a single hard disk, or have a hard disk failure, simply logon as admin and select Disk Redundancy to add a new drive to your RAID1 array.
But with the best laid plans things don't always goaccording to plan, these are the processes required to do it manually
HowTo: Manage/Check a RAID1 Array from the command Line
What is the Status of the Array
[root@ ~]# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb2[2] sda2[0]
488279488 blocks [2/1] [U_]
[=>...................] recovery = 6.3% (31179264/488279488) finish=91.3min speed=83358K/sec
md1 : active raid1 sdb1[1] sda1[0]
104320 blocks [2/2] [UU]
unused devices: <none>
Are the Disk Partitioned Correctly ?
Here two disks are partitioned identically
[root@ ~]# fdisk -lu /dev/sda; fdisk -lu /dev/sdb Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors Units = sectors of 1 * 512 = 512 bytes Device Boot Start End Blocks Id System /dev/sda1 * 63 208844 104391 fd Linux raid autodetect /dev/sda2 208845 1953520064 976655610 fd Linux raid autodetect Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors Units = sectors of 1 * 512 = 512 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 63 208844 104391 fd Linux raid autodetect /dev/sdb2 208845 1953520064 976655610 fd Linux raid autodetect
Example : Incorrecty Partitioned 2nd Disk
In this example the partitions are set too close to the start of the disk and there is no room for GRUB to be written, the disk will not boot, there will not be enough room for grub staging
[root@ ~]# fdisk -l /dev/sdb; fdisk -lu /dev/sdb Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 13 104384+ fd Linux raid autodetect Partition 1 does not end on cylinder boundary. /dev/sdb2 13 121601 976655647 fd Linux raid autodetect Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors Units = sectors of 1 * 512 = 512 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 208769 104384+ fd Linux raid autodetect Partition 1 does not end on cylinder boundary. /dev/sdb2 208770 1953520063 976655647 fd Linux raid autodetect
message Log showing Grub errors
add_drive_to_raid: Waiting for boot partition to sync before installing grub... add_drive_to_raid: Probing devices to guess BIOS drives. This may take a long time. add_drive_to_raid: add_drive_to_raid: add_drive_to_raid: GNU GRUB version 0.95 (640K lower / 3072K upper memory) add_drive_to_raid: add_drive_to_raid: [ Minimal BASH-like line editing is supported. For the first word, TAB add_drive_to_raid: lists possible command completions. Anywhere else TAB lists the possible add_drive_to_raid: completions of a device/filename.] add_drive_to_raid: grub> device (hd0) /dev/sdb add_drive_to_raid: grub> root (hd0,0) add_drive_to_raid: Filesystem type is ext2fs, partition type 0xfd add_drive_to_raid: grub> setup (hd0) add_drive_to_raid: Checking if "/boot/grub/stage1" exists... no add_drive_to_raid: Checking if "/grub/stage1" exists... yes add_drive_to_raid: Checking if "/grub/stage2" exists... yes add_drive_to_raid: Checking if "/grub/e2fs_stage1_5" exists... yes add_drive_to_raid: Running "embed /grub/e2fs_stage1_5 (hd0)"... failed (this is not fatal) add_drive_to_raid: Running "embed /grub/e2fs_stage1_5 (hd0,0)"... failed (this is not fatal) add_drive_to_raid: Running "install /grub/stage1 (hd0) /grub/stage2 p /grub/grub.conf "... succeeded add_drive_to_raid: Done. add_drive_to_raid: grub> quit
HowTo: Remove a disk from the RAID1 Array from the command Line
Look at the mdstat
[root@ ~]# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb2[1] sda2[0]
488279488 blocks [2/2] [UU]
md1 : active raid1 sdb1[1] sda1[0]
104320 blocks [2/2] [UU]
unused devices: <none>
Fail and remove the disk, sdb in this case
[root@ ~]# mdadm --manage /dev/md2 --fail /dev/sdb2 mdadm: set /dev/sdb2 faulty in /dev/md2 [root@ ~]# mdadm --manage /dev/md2 --remove /dev/sdb2 mdadm: hot removed /dev/sdb2 [root@ ~]# mdadm --manage /dev/md1 --fail /dev/sdb1 mdadm: set /dev/sdb1 faulty in /dev/md1 [root@ ~]# mdadm --manage /dev/md1 --remove /dev/sdb1 mdadm: hot removed /dev/sdb1
Add the partitions back
[root@ ~]# mdadm --manage /dev/md1 --add /dev/sdb1 mdadm: hot added /dev/sdb1 [root@ ~]# mdadm --manage /dev/md2 --add /dev/sdb2 mdadm: hot added /dev/sdb2
HowTo: Partition / Re-Partition, this disk
Delete Existing Partitions
[root@ ~]# fdisk /dev/sdb The number of cylinders for this disk is set to 121601. 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: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 13 104384+ fd Linux raid autodetect Partition 1 does not end on cylinder boundary. /dev/sdb2 13 121601 976655647 fd Linux raid autodetect Command (m for help): d Partition number (1-4): 1 Command (m for help): d Selected partition 2 Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
Create new partitions
Note: change the partitions system id to reflect Linux raid autodetect
[root@ ~]# fdisk /dev/sdb The number of cylinders for this disk is set to 121601. 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): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-121601, default 1): Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-121601, default 121601): 13 Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 2 First cylinder (14-121601, default 14): Using default value 14 Last cylinder or +size or +sizeM or +sizeK (14-121601, default 121601): Using default value 121601 Command (m for help): a Partition number (1-4): 1 Command (m for help): t Partition number (1-4): 1 Hex code (type L to list codes): fd Changed system type of partition 1 to fd (Linux raid autodetect) 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): p Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 13 104391 fd Linux raid autodetect /dev/sdb2 14 121601 976655610 fd Linux raid autodetect Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
HowTo: Write the GRUB boot sector
[root@ ~]# grub
GNU GRUB version 0.95 (640K lower / 3072K upper memory)
[ Minimal BASH-like line editing is supported. For the first word, TAB
lists possible command completions. Anywhere else TAB lists the possible
completions of a device/filename.]
grub> device (hd0) /dev/sdb
grub> root (hd0,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... no
Checking if "/grub/stage1" exists... yes
Checking if "/grub/stage2" exists... yes
Checking if "/grub/e2fs_stage1_5" exists... yes
Running "embed /grub/e2fs_stage1_5 (hd0)"... 16 sectors are embedded.
succeeded
Running "install /grub/stage1 (hd0) (hd0)1+16 p (hd0,0)/grub/stage2 /grub/grub.conf"... succeeded
Done.
grub> quit
My Experience
My experience is loosely alluded to above, I upgraded the disk in a Dell server with two new Seagate 1Tb ST1000340NS from the 500Gb that came with the server, they are a Server Edition disk.
The Disks were installed separately and allowed to come up and sync in the array, the first indication that something wasn't working was the machine would not boot when the 2nd disk was installed. I set back my original first disk and looked through the system log, noting th grub failures. It's not fatal was the message, but it did stop the machine from booting on the disk, perhaps that's just not living, therefore not fatal, whatever, it's not terribly useful. It did this on both disks.
What has happened is that disk partition was written too close to the start of the drive, so the boot record didn't have enough room for its GRUB staging - if thats the right term.
To correct this, I removed the disk from the array, by failing it, then remove it, then repartitioning and add it back to the array.
David Bray
17 March, 2010