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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ATARAID(4) BSD Kernel Interfaces Manual ATARAID(4)
NAME
ataraid -- ATA software RAID support
SYNOPSIS
device ata
device ataraid
DESCRIPTION
The ataraid driver provides support for so-called software RAID (sometimes referred to as fake RAID or pseudo RAID).
When a controller that supports software RAID is instructed to create a RAID array, its BIOS writes data structures in a specific metadata
format to the disks. These data structures are picked up by the ataraid driver, so that FreeBSD can work with the array. The ataraid driver
has to understand the specific metadata format of a controller BIOS in order to support its RAID capabilities.
Read-only support for a metadata format means that FreeBSD can use the given RAID array for normal read/write operations. Creation and
rebuild of such arrays has to be done from the controller BIOS.
Read and write support for a metadata format means that FreeBSD can use the given RAID array for normal read/write operations. Additionally,
the atacontrol(8) utility can be used to create, rebuild, update and fail such RAID arrays.
The ataraid driver can read the following metadata formats:
o Adaptec HostRAID
o Highpoint V2 RocketRAID
o Highpoint V3 RocketRAID
o Intel MatrixRAID
o Integrated Technology Express (ITE)
o JMicron
o LSI Logic V2 MegaRAID
o LSI Logic V3 MegaRAID
o NVIDIA MediaShield
o Promise FastTrak
o Silicon Image Medley
o Silicon Integrated Systems (SiS)
o VIA Tech V-RAID
o FreeBSD PseudoRAID
The ataraid driver can write the following metadata formats:
o Highpoint V2 RocketRAID
o Intel MatrixRAID
o JMicron
o Promise FastTrak
o Silicon Integrated Systems (SiS)
o VIA Tech V-RAID
o FreeBSD PseudoRAID
It is also possible to use software RAID on controllers that do not have special software RAID capabilities. See atacontrol(8) for details.
FILES
/dev/ar* ATA RAID device nodes
SEE ALSO
ata(4), atacontrol(8)
CAVEATS
RAID5 is not supported at this time. Code exists, but it neither uses nor maintains parity information.
AUTHORS
The ataraid driver was written by Soren Schmidt <sos@FreeBSD.org>. This manual page was written by Christian Brueffer
<brueffer@FreeBSD.org>.
BSD
February 17, 2006 BSD