HP Surestore E Disk Array XP256 HP XP P9000 External Storage Access Manager Us - Page 17

Preventing unnecessary failover, Sharing volumes with other HP software products, At this time

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It is possible that maintenance operations require both storage systems to be powered off at the same time. In this case, the health checking periods would be shortened to prevent unexpected failover while both systems are powered off. After failover, when a failure is corrected, you may continue operations on the S-VOL, though HP recommends switching them back to the P-VOL. To find which volume was originally a P-VOL, use the multipath software on the host to refer to path information, checking for the volume with the owner path. The owner path is set to the volume that you specified as a P-VOL when you created an ESAM pair. The owner path never switches even if the P-VOL and S-VOL were swapped due to a failover. Preventing unnecessary failover Some applications issue the read command to the ESAM S-VOL. When these applications are used, and when the number of read commands to the S-VOL reaches or exceeds the threshold (1,000 times per six minutes), ESAM assumes that a P-VOL failure has occurred. This situation results in an unnecessary failover to the ESAM S-VOL. At this time, the Solaris VERITAS Volume Manager (VxVM) vxdisksetup command issues more read commands than allowed by the threshold. You can prevent unnecessary failover by setting host mode option 48 to ON. Note that when this option is ON, the S-VOL responds slower to the read command. Review system conditions and resulting behaviors related to host mode option 48 in the following table. Table 1 System behavior for host mode option 48 Event Normal operation. The S-VOL receives more read commands than allowed by the threshold, and receives no write command. Behavior when OFF Behavior when ON Failover occurs only when you run certain No failover, even when you run the applications. applications. • Updates from a host go to S-VOL, and S-VOL status becomes SSWS. • The S-VOL responds to the read command as quickly as the P-VOL responds. • Updates from a host go to P-VOL, and S-VOL status remains PAIR. • The S-VOL responds slower to the read command than the P-VOL does. The S-VOL takes several milliseconds to respond. The S-VOL receives one or more write commands. • Updates from a host go to S-VOL, and S-VOL status becomes SSWS. • The S-VOL responds to the read command as quickly as the P-VOL responds. Same as when option 48 is OFF. For more information about setting host mode options, see the HP XP P9000 Provisioning for Open Systems User Guide. Sharing volumes with other HP software products ESAM volumes can be used as volumes for other HP software products, such as Business Copy or Virtual LUN. The following table shows the ESAM volumes that can be shared with other software. Only those volumes listed can be shared. Preventing unnecessary failover 17

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It is possible that maintenance operations require both storage systems to be powered off at the
same time. In this case, the health checking periods would be shortened to prevent unexpected
failover while both systems are powered off.
After failover, when a failure is corrected, you may continue operations on the S-VOL, though HP
recommends switching them back to the P-VOL. To find which volume was originally a P-VOL, use
the multipath software on the host to refer to path information, checking for the volume with the
owner path. The owner path is set to the volume that you specified as a P-VOL when you created
an ESAM pair. The owner path never switches even if the P-VOL and S-VOL were swapped due
to a failover.
Preventing unnecessary failover
Some applications issue the read command to the ESAM S-VOL. When these applications are
used, and when the number of read commands to the S-VOL reaches or exceeds the threshold
(1,000 times per six minutes), ESAM assumes that a P-VOL failure has occurred. This situation
results in an unnecessary failover to the ESAM S-VOL.
At this time, the Solaris VERITAS Volume Manager (VxVM)
vxdisksetup
command issues more
read commands than allowed by the threshold.
You can prevent unnecessary failover by setting host mode option 48 to ON. Note that when this
option is ON, the S-VOL responds slower to the read command.
Review system conditions and resulting behaviors related to host mode option 48 in the following
table.
Table 1 System behavior for host mode option 48
Behavior when ON
Behavior when OFF
Event
No failover, even when you run the
applications.
Failover occurs only when you run certain
applications.
Normal operation.
The S-VOL receives more
read commands than
•
Updates from a host go to P-VOL, and
S-VOL status remains PAIR.
•
Updates from a host go to S-VOL, and
S-VOL status becomes SSWS.
allowed by the threshold,
•
•
The S-VOL responds to the read
command as quickly as the P-VOL
responds.
The S-VOL responds slower to the read
command than the P-VOL does. The
S-VOL takes several milliseconds to
respond.
and receives no write
command.
Same as when option 48 is OFF.
The S-VOL receives one or
more write commands.
•
Updates from a host go to S-VOL, and
S-VOL status becomes SSWS.
•
The S-VOL responds to the read
command as quickly as the P-VOL
responds.
For more information about setting host mode options, see the
HP XP P9000 Provisioning for Open
Systems User Guide
.
Sharing volumes with other HP software products
ESAM volumes can be used as volumes for other HP software products, such as Business Copy or
Virtual LUN.
The following table shows the ESAM volumes that can be shared with other software. Only those
volumes listed can be shared.
Preventing unnecessary failover
17