HP XP Racks - Manual (Page 7)

1 External Storage Access Manager overview
ESAM ensures high availability of host applications used in P9500 (P9500) storage systems. ESAM
provides protection against the loss of application availability when input and output (I/O) failures
occur in the primary storage system by automatically switching host applications from the primary
storage system to the secondary storage system and by enabling recovery from the failures that
caused the I/O failure.
ESAM is designed for recovery from on-site disasters such as power supply failure. Continuous
Access Synchronous is suited to large-scale disaster recovery.
How ESAM works
ESAM uses Continuous Access Synchronous software to create a synchronous remote copy of a
production volume. But where Continuous Access Synchronous is suited to large-scale disaster
recovery, ESAM is intended for recovery from on-sight disasters such as power supply failure.
Because of this, ESAM is configured differently than a typical Continuous Access Synchronous
configuration.
•
The ESAM primary and secondary storage systems are connected to the same host. When
an ESAM pair is created, the host sees the primary and secondary volumes as the same
volume.
•
ESAM requires multipath software to be installed on the host. In the event that the host cannot
access the production volume on the primary storage system, host I/O is redirected via the
host multipath software to the secondary volume on the remote system. Failover is accomplished
without stopping and restarting the application.
•
ESAM is used on open host systems only.
•
An ESAM pair consists of a primary data volume (P-VOL) on the primary storage system and
a secondary data volume (S-VOL) on the secondary storage system (like Continuous Access
Synchronous). The S-VOL is the copy of the P-VOL.
•
ESAM uses a quorum disk located on an external storage system, which keeps track of
consistency between the P-VOL and S-VOL. Consistency data is used in the event of an
unexpected outage of the data path or primary storage system. In this case, the differential
data in both systems is compared and, if the pairs are consistent, host operations continue on
the secondary storage system.
How ESAM works 7