Technical data

For example, in a typical configuration, a Linux host with a dual por t HBA is connected to an EVA
4000 through two switches. In this case, if all the paths are available, the host has four I/O paths
for any LUN presented from the EVA 4000. The multipath.conf file enables the host to view the
multipath map, as follows:
3600508b30090f5d0cf46bd1a4c420023
[size=1 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [prio=100][active]
\_ 3:0:1:3 sdad 65:208 [active][ready]
\_ 2:0:2:3 sdo 8:224 [active][ready]
\_ round-robin 0 [prio=20][enabled]
\_ 2:0:1:3 sdj 8:144 [active][ready]
\_ 3:0:0:3 sdy 65:128 [active][ready]
3600508b30090f5d0d2a9d64590490022
[size=3 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [prio=120][active]
\_ 3:0:2:4 sdaj 66:48 [active][ready]
\_ 3:0:3:4 sdao 66:128 [active][ready]
\_ 2:0:0:4 sdf 8:80 [active][ready]
\_ 2:0:3:4 sdu 65:64 [active][ready]
Path Grouping
The information in the map is presented by grouping the paths for a LUN with u nique identifiers, such
as UID/WWN.The size, features, and the corresponding hwhandlers are displayed followed
by the unique LUN identifier.
The grouping of paths is d one and p resented in a map based on the I/O load balancing policy. In the
above example, for the LUN 3600508b30090f5d0d2a9d64590490022, the grouping is done with
the policy as
multibus and the devices, such as sdaj, sdao, sdf,andsdu belong to same path group.
The state of t
he group is either active or enabled depending on whether I/O is a ctive or not.
For the LUN 3600508b30090f5d0cf46bd1a4c420023, the grouping is done with the policy as
group_by_prio.
The devices s
dad and sdo belong to one path group, and the devices sdj and sdy belong to a
different p
ath group, because they are from two controllers with different serial numbers.
The I/O alwa
ys happens in the path group which is active. If all paths in the active group fails, the
failover oc
curs to the other path group that i s enabled on changing that path group to active. When the
paths are u
p again and the failback parameter is set as immediate, the failback occurs to the earlier
group and I
/O occurs through the earlier group.
Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays
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