Managing Multipath I/O for Devices
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The devices should now be listed in
/dev/disk/by-id
, and have symbolic links to
their Device Mapper device names. For example:
lrwxrwxrwx 1 root root 10 Jun 15 09:36 scsi-mpath1 -> ../../dm-1
6
Restart the
boot.md
service and the RAID device by entering
/etc/init.d/boot.md start
7
Check the status of the software RAID by entering
mdadm --detail /dev/md0
The RAID’s component devices should match their Device Mapper device names that are listed
as the symbolic links of devices in the
/dev/disk/by-id
directory.
8
Make a new
initrd
to ensure that the Device Mapper
multipath
services are loaded
before the
md
RAID services on reboot. Enter
mkinitrd -f mpath
9
Reboot the server to apply these post-install configuration settings.
10
Verify that the software RAID array comes up properly on top of the multipathed devices by
checking the RAID status. Enter
mdadm --detail /dev/md0
For example:
Number Major Minor RaidDevice State
0 253 0 0 active sync /dev/dm-0
1 253 1 1 active sync /dev/dm-1
2 253 2 2 active sync /dev/dm-2
5.12 Using Multipathed Devices
Multipathed devices can be used directly, with LVM, and with
mdadm
.
Section 5.12.1, “Using the Devices Directly,” on page 53
Section 5.12.2, “Using LVM2,” on page 53
Section 5.12.3, “Using mdadm,” on page 54
Section 5.12.4, “Partitions,” on page 54
5.12.1 Using the Devices Directly
If you want to use the entire LUNs directly (for example, if you are using the SAN features to
partition your storage), you can simply use the
/dev/disk/by-id/xxx
names directly for
mkfs
,
fstab
, your application, etc.
5.12.2 Using LVM2
To make LVM2 recognize the multipathed devices as possible physical volumes, you must modify
/
etc/lvm/lvm.conf
. It is important to modify it in a way that it does not scan and use the
physical paths, but only accesses the multipath I/O storage through the multipath I/O layer. To do so,
change the
filter
and
types
entry in
/etc/lvm/lvm.conf
as follows:
filter = [ "a|/dev/disk/by-id/.*|", "r|.*|" ]
types = [ "device-mapper", 253 ]
Summary of Contents for LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007
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