Chapter 12. Host configuration 563
Example 12-21 shows this verification.
Example 12-21 sdd run level example
[root@Palau sdd]# chkconfig --list sdd
sdd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
[root@Palau sdd]#
If necessary, you can disable the start-up option by entering this command:
chkconfig sdd off
Run the datapath query commands to display the online adapters and the paths to the
adapters. Notice that the preferred paths are used from one of the nodes, that is, path 0 and
path 2. Path 1 and path 3 connect to the other node and are used as alternate or backup
paths for high availability, as shown in Example 12-22.
Example 12-22 datapath query command example
[root@Palau ~]# datapath query adapter
Active Adapters :2
Adpt# Name State Mode Select Errors Paths Active
0 Host0Channel0 NORMAL ACTIVE 1 0 2 0
1 Host1Channel0 NORMAL ACTIVE 0 0 2 0
[root@Palau ~]#
[root@Palau ~]# datapath query device
Total Devices : 1
DEV#: 0 DEVICE NAME: vpatha TYPE: 2145 POLICY: Optimized Sequential
SERIAL: 60050768018201bee000000000000035
============================================================================
Path# Adapter/Hard Disk State Mode Select Errors
0 Host0Channel0/sda CLOSE NORMAL 1 0
1 Host0Channel0/sdb CLOSE NORMAL 0 0
2 Host1Channel0/sdc CLOSE NORMAL 0 0
3 Host1Channel0/sdd CLOSE NORMAL 0 0
[root@Palau ~]#
SDD has three path-selection policy algorithms:
Failover only (fo): All I/O operations for the device are sent to the same (preferred) path
unless the path fails because of I/O errors. Then, an alternate path is chosen for
subsequent I/O operations.
Load balancing (lb): The path to use for an I/O operation is chosen by estimating the load
on the adapter to which each path is attached. The
load is a function of the number of I/O
operations currently in process. If multiple paths have the same load, a path is chosen at
random from those paths. Load-balancing mode also incorporates failover protection. The
load-balancing policy is also known as the
optimized policy.
Round-robin (rr): The path to use for each I/O operation is chosen at random from paths
that were not used for the last I/O operation. If a device has only two paths, SDD
alternates between the two paths.
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