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Top Forums UNIX for Advanced & Expert Users Identify failed disk in Linux RAID Post 302562352 by Loic Domaigne on Thursday 6th of October 2011 03:04:10 PM
Old 10-06-2011
Identify failed disk in Linux RAID

Good Evening,

2 years ago, I set up an Ubuntu file-server for a friend, who is a photograph amateur. Basically, the server offers a software RAID-5 that can be accessed remotely from a MAC. Unfortunately, I didn't labeled the hard drives (i.e. which physical drive corresponds to the /dev/sdX device).

Now a drive has failed, and the RAID-5 is at risk. I needed to find out which physical drive we have to replace, before we can rebuild the array. I have summed up below the procedure I'd follow. It would be great if some Linux software RAID connaisseur could review it. The more eyeballs, the better; and beside Linux RAID are quite new land for me.

1. stop raid system
# umount /dev/md1
# mdadm -S /dev/md1

2. Unplug one by one the hard drives. Looks in dmesg failure events for /dev/sdX. That way the mapping between the physical disk and the device /dev/sdX is step-by-step revealed.

3. Replace the failed disk, and partition it accordingly to what is expected.

4. Rebuild the mirror with the new disk
- get UUID with mdadm -query
- assemble array with that new disk: mdadm --assemble /dev/md -u XXX
- update /etc/mdadm.conf: mdadm --detail --scan >> /etc/mdadm.conf

You find below detailed information about the server set-up.

TIA,
Loïc

The setup:

Ubuntu server, 6 SATA Hard drives /dev/sda ... /dev/sdf

Each Drives (X=a..f) are partitioned as followed:
/sdX1 type Linux Partition
/sdX2 type swap
/sdX3 type extended
/sdX5 type RAID


The server has 2 software Raids:
/dev/md0 RAID1 /sda1 and /sdb1
/dev/md1 RAID5 /sda5, /sdb5, /sdc5, /sdd5, /sde5, /sdf5

The OS is located on /dev/md0, only application data are located on /dev/md1

The Failure:

A Fail event had been detected on md device /dev/md1.
It could be related to component device /dev/sdd5.
The /proc/mdstat file currently contains the following:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid5 sde5[4] sdc5[2] sdd5[6](F) sdf5[5] sdb5[1] sda5[0]
9636429120 blocks level 5, 64k chunk, algorithm 2 [6/5] [UUU_UU]

md0 : active raid1 sdb1[1] sda1[0]
20506816 blocks [2/2] [UU]


unused devices: <none>
 

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HD(4)							     Linux Programmer's Manual							     HD(4)

NAME
hd - MFM/IDE hard disk devices DESCRIPTION
The hd* devices are block devices to access MFM/IDE hard disk drives in raw mode. The master drive on the primary IDE controller (major device number 3) is hda; the slave drive is hdb. The master drive of the second controller (major device number 22) is hdc and the slave hdd. General IDE block device names have the form hdX, or hdXP, where X is a letter denoting the physical drive, and P is a number denoting the partition on that physical drive. The first form, hdX, is used to address the whole drive. Partition numbers are assigned in the order the partitions are discovered, and only nonempty, nonextended partitions get a number. However, partition numbers 1-4 are given to the four partitions described in the MBR (the "primary" partitions), regardless of whether they are unused or extended. Thus, the first logi- cal partition will be hdX5. Both DOS-type partitioning and BSD-disklabel partitioning are supported. You can have at most 63 partitions on an IDE disk. For example, /dev/hda refers to all of the first IDE drive in the system; and /dev/hdb3 refers to the third DOS "primary" partition on the second one. They are typically created by: mknod -m 660 /dev/hda b 3 0 mknod -m 660 /dev/hda1 b 3 1 mknod -m 660 /dev/hda2 b 3 2 ... mknod -m 660 /dev/hda8 b 3 8 mknod -m 660 /dev/hdb b 3 64 mknod -m 660 /dev/hdb1 b 3 65 mknod -m 660 /dev/hdb2 b 3 66 ... mknod -m 660 /dev/hdb8 b 3 72 chown root:disk /dev/hd* FILES
/dev/hd* SEE ALSO
chown(1), mknod(1), sd(4), mount(8) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 1992-12-17 HD(4)
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