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D Using Veritas Cluster Server to prevent data corruption

Using VCS I/O fencing

By issuing a Persistent Reserve SCSI-3 command, VCS employs an I/O fencing feature that prevents

data corruption from occurring if cluster communication stops. To accomplish I/O fencing, each

node of VCS registers reserve keys for each disk in a disk group that is imported. The reserve key

consists of a unique value for each disk group and a value to distinguish nodes. When importing

a disk group, each node in a VCS cluster registers the reserve key for all paths of all disks (LUs)

in the disk group, but only 1 node will succeed in reserving the disk group. Example reserve keys

for Port 1A are shown in “Port 1A Key Registration Entries” (page 148) and example reserve keys

for Port 2A are shown in “Port 2A Key Registration Entries” (page 148). The format of the reserve

key is:

node number + disk group-unique information

When the Persistent Reserve command is received by the disk array, the reserve key and Port

WWN of node are registered in the key registration table for each port of the disk array. To avoid

duplicate registrations, the disk array checks the node Port WWN and reserve key and only adds

an entry in its table if the WWN/reserve key combination do not already exist in the table for the

port which received the registration request. Duplicate entries can exist across different ports.

The maximum number of reserve keys that can be registered per port for each disk array is 128.

Attempts to add additional registration keys will fail if the number exceeds this limit. Because of

this, try to limit the number of:

• Nodes

• Paths to each array port

• Disk groups

For example, when adding an LU to increase disk capacity, do not create a new disk group.

Instead, add the LU to one of the existing disk groups (see “Nodes and ports” (page 147)).

For each array port, calculate the number of VCS registration keys needed as follows:

number of WWNs visible to a HP XP7 port x number of disk groups = number of

registration keys

Where the number of WWNs visible to a HP XP7 port = number of hosts x number

of WWNs per HP XP7 port.

In “Nodes and ports” (page 147), the number of WWNs visible to either port (1A or 2A) is four

(WWNa0 and WWNb0 for port 1A and WWNa1 and WWNb1 for port 2A). Therefore, the

number of registration keys will be equal to 4.

146 Using Veritas Cluster Server to prevent data corruption

HP XP7 Configuration Guide

Other manuals for HP XP7