Installation guide

Raid Level : raid0
Array Size : 15621632 (14.90 GiB 15.100 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Mon Mar 1 13:49:10 2004
State : dirty, no-errors
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Chunk Size : 64K
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
2 8 33 2 active sync /dev/sdc1
3 8 49 3 active sync /dev/sdd1
UUID : 25c0f2a1:e882dfc0:c0fe135e:6940d932
Events : 0.1
3.2. Creating a Multipath Device With mdadm
In addition to creating RAID arrays, mdadm can also be used to take advantage of hardware sup-
porting more than one I/O path to individual SCSI LUNs (disk drives). The goal of multipath stor-
age is continued data availability in the event of hardware failure or individual path saturation.
Because this configuration contains multiple paths (each acting as an independent virtual con-
troller) accessing a common SCSI LUN (disk drive), the Linux kernel detects each shared drive
once "through" each path. In other words, the SCSI LUN (disk drive) known as /dev/sda may
also be accessible as /dev/sdb, /dev/sdc, and so on, depending on the specific configuration.
To provide a single device that can remain accessible if an I/O path fails or becomes saturated,
mdadm includes an additional parameter to its level option. This parameter multipath directs the
md layer in the Linux kernel to re-route I/O requests from one pathway to another in the event of
an I/O path failure.
To create a multipath device, edit the /etc/mdadm.conf file to define values for the DEVICE and
ARRAY lines that reflect your hardware configuration.
Note
Unlike the previous RAID example (where each device specified in /
etc/mdadm.conf must represent different physical disk drives), each device in this
file refers to the same shared disk drive.
The command used for the creation of a multipath device is similar to that used to create a
RAID device; the difference is the replacement of a RAID level parameter with the multipath
parameter:
mdadm -C /dev/md0 --level=multipath --raid-devices=4 /dev/sda1 /dev/sdb1
/dev/sdc1 /dev/sdd1
Continue creating array? yes
3.2. Creating a Multipath Device With mdadm
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