|
September 2015 Data written by the host
systems is sent synchronously to the two physical volumes by the Loxoll HAE.
Good completion status for each write command is sent to the host system only
after good completion status is received from both physical volumes making up
the mirrored drive (i.e. both members). In
addition to providing protection against data unavailability or loss, the
identical, mirrored members are also used by the HAE to accelerate read
performance to a level that is higher than what can be provided by a single
member alone. By alternately reading from each member in round-robin fashion,
read performance gain often can approach a factor of two. Two
physical storage volumes are encapsulated and presented as one
host-accessible logical disk. The two members comprising the mirror drive are
invisible to hosts, and are completely managed by HAE. Only mirrored drives,
and not their individual members, are exposed to hosts by the HAEs. In the event of mirroring
between a higher-performance and a lower-performance storage system, it is
possible to specify that the higher-performance member should be preferred
for reading. In this case all reads will be directed to the higher-performance
member (as long as it is available). This approach can also be used when
mirroring over distance in order to minimize traffic through the
long-distance connection. To be continued … |
Questions?
If you have questions
about high availability solutions or this article, please contact us at:
Newsletter
Archive Click here to visit our newsletter
archive library. |