IBM Storwize V5020 User Manual

500 Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1
10.3.7 Summary of the FlashCopy indirection layer algorithm
Table 10-2 summarizes the indirection layer algorithm.
Table 10-2 Summary table of the FlashCopy indirection layer algorithm
10.3.8 Interaction with the cache
Starting with V7.3, the entire cache subsystem was redesigned and changed. Cache has
been divided into upper and lower cache. Upper cache serves mostly as write cache and
hides the write latency from the hosts and application. Lower cache is a read/write cache and
optimizes I/O to and from disks. Figure 10-8 shows the new IBM Spectrum Virtualize cache
architecture.
Figure 10-8 New cache architecture
Accessed
volume
Was the grain
copied?
Host I/O operation
Read Write
Source No Read from the source
volume.
Copy grain to most recently
started target for this source,
then write to the source.
Yes Read from the source
volume.
Write to the source volume.
Target No If any newer targets exist for
this source in which this grain
was copied, read from the
oldest of these targets.
Otherwise, read from the
source.
Hold the write. Check the
dependency target volumes
to see whether the grain was
copied. If the grain is not
copied to the next oldest
target for this source, copy
the grain to the next oldest
target. Then, write to the
target.
Yes Read from the target volume. Write to the target volume.

IBM Storwize V5020 Specifications

General

Brand	IBM
Model	Storwize V5020
Category	Storage
Language	English