Red Hat Enterprise Linux Installation Guide 5.2 - linux.meuhobby.com

Chapter 22. Additional Information for IBM System z Users
mdadm: array /dev/md0 started.
Due to the length of the mdadm command line, it has been broken into two lines.
In this example, the hardware consists of one SCSI LUN presented as four separate SCSI
devices, each accessing the same storage by a different pathway. Once the multipath device
/dev/md0 is created, all I/O operations referencing /dev/md0 are directed to /dev/sda1,
/dev/sdb1, /dev/sdc1, or /dev/sdd1 (depending on which path is currently active and
operational).
The configuration of /dev/md0 can be examined more closely using the command mdadm
--detail /dev/md0 to verify that it is, in fact, a multipath device:
/dev/md0:
Version : 00.90.00
Creation Time : Tue Mar 2 10:56:37 2004
Raid Level : multipath
Array Size : 3905408 (3.72 GiB 3.100 GB)
Raid Devices : 1
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Tue Mar 2 10:56:37 2004
State : dirty, no-errors
Active Devices : 1
Working Devices : 4
Failed Devices : 0
Spare Devices : 3
Number Major Minor RaidDevice State
0 8 49 0 active sync /dev/sdd1
1 8 17 1 spare /dev/sdb1
2 8 33 2 spare /dev/sdc1
3 8 1 3 spare /dev/sda1
UUID : 4b564608:fa01c716:550bd8ff:735d92dc
Events : 0.1
Another feature of mdadm is the ability to force a device (be it a member of a RAID array or a
path in a multipath configuration) to be removed from an operating configuration. In the
following example, /dev/sda1 is flagged as being faulty, is then removed, and finally is added
back into the configuration. For a multipath configuration, these actions would not affect any I/O
activity taking place at the time:
# mdadm /dev/md0 -f /dev/sda1
mdadm: set /dev/sda1 faulty in /dev/md0
# mdadm /dev/md0 -r /dev/sda1
mdadm: hot removed /dev/sda1
# mdadm /dev/md0 -a /dev/sda1
mdadm: hot added /dev/sda1
#
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