Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS, Administration Manual

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66 SLES 10 Storage Administration Guide for EVMS
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can survive a single disk failure at a time. A RAID 4 can survive a single disk failure at a time if the
disk is not the parity disk.
Disks can fail for many reasons such as the following:
Š
Disk crash
Š Disk pulled from the system
Š
Drive cable removed or loose
Š I/O errors
When a disk fails, the RAID removes the failed disk from membership in the RAID, and operates in
a degraded mode until the failed disk is replaced by a spare. Degraded mode is resolved for a single
disk failure in one of the following ways:
Š
Spare Exists: If the RAID has been assigned a spare disk, the MD driver automatically
activates the spare disk as a member of the RAID, then the RAID begins synchronizing (RAID
1) or reconstructing (RAID 4 or 5) the missing data.
Š
No Spare Exists: If the RAID does not have a spare disk, the RAID operates in degraded mode
until you configure and add a spare. When you add the spare, the MD driver detects the RAID’s
degraded mode, automatically activates the spare as a member of the RAID, then begins
synchronizing (RAID 1) or reconstructing (RAID 4 or 5) the missing data.
6.5.2 Identifying the Failed Drive
On failure,
md
automatically removes the failed drive as a component device in the RAID array. To
determine which device is a problem, use
mdadm
and look for the device that has been reported as
“removed”.
1 Enter the following a a terminal console prompt
mdadm -D /dev/md1
Replace
/dev/md1
with the actual path for your RAID.
For example, an
mdadm
report for a RAID 1 device consisting of
/dev/sda2
and
/dev/sdb2
might look like this:
blue6:~ # mdadm -D /dev/md1
/dev/md1:
Version : 00.90.03
Creation Time : Sun Jul 2 01:14:07 2006
Raid Level : raid1
Array Size : 180201024 (171.85 GiB 184.53 GB)
Device Size : 180201024 (171.85 GiB 184.53 GB)
Raid Devices : 2
Total Devices : 1
Preferred Minor : 1
Persistence : Superblock is persistent
Update Time : Tue Aug 15 18:31:09 2006
State : clean, degraded
Active Devices : 1
Working Devices : 1