Download Implementing the IBM Storwize V3700

Adding this technology at each end of a WAN Transmission Control Protocol/Internet Protocol
(TCP/IP) link significantly improves the utilization of the link. It does this by applying patented
artificial intelligence (AI) to hide latency normally associated with WANs. Instead, the
Storwize technology uses TCP/IP latency to its advantage. In a traditional IP link performance
drops off as more data is sent, because each transmission must wait for acknowledgment
before the next can be sent.
Rather than wait for the acknowledgment to come back, the Storwize technology sends more
sets of packets across other virtual connections. The number of virtual connections is
controlled by the AI engine. This improves WAN connection use, which results in a data
transfer rate approaching full line speed, and is similar to the use of buffer-to-buffer credits
in FC.
If packets are lost from any virtual connection, the data is retransmitted, and the remote unit
waits for it. Presuming that this is not a frequent problem, overall performance is only
marginally affected because of the delay of an extra round trip for the data that is resent. The
implementation of this technology can greatly improve the performance of Remote Copy,
especially Global Mirror with Change Volumes over long distances.
For more information about Native IP replication and how to use it, see the separate
publication:
IBM SAN Volume Controller and Storwize Family Native IP Replication, REDP-5103
Interaction between Remote Copy and FlashCopy
Table 10-5 lists which combinations of FlashCopy and Remote Copy are supported.
Table 10-5 FlashCopy and Remote Copy interaction
Component
Remote Copy primary
Remote Copy secondary
FlashCopy source
Supported
Supported.
When the FlashCopy
relationship is in the Preparing
and Prepared states, the cache
at the Remote Copy secondary
site operates in write-through
mode. This process adds more
latency to the already-latent
Remote Copy relationship.
FlashCopy target
This combination is supported
and has the following
restrictions:
򐂰 Running stop -force
might cause the Remote
Copy relationship to fully
resynchronize.
򐂰 The I/O group must be the
same.
This combination is supported
by the restriction that the
FlashCopy mapping cannot be
copying, stopping, or
suspended. Otherwise, the
restrictions are the same as at
the Remote Copy primary site.
If you are not using Global Mirror with Change Volumes, for disaster recovery purposes, you
can use the FlashCopy feature to create a consistent copy of an image before you restart a
Global Mirror relationship.
528
Implementing the IBM Storwize V3700