Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION, Installation Manual

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Configuring IPL from a SCSI Device
237
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, no­errors
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
#
22.4. Configuring IPL from a SCSI Device
Anaconda (the installation program) supports the direct installation to SCSI devices. This section
includes information on how to IPL from a SCSI device within z/VM.