Hitachi Virtual Storage Platform, Руководство пользователя и справочник

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Hitachi VSP User and Reference Guide
3–14
System Components
Memory operation
The Virtual Storage Platform places all read and write data in the cache. The
amount of fast-write data in cache is dynamically managed by the cache
control algorithms to provide the optimum amount of read and write cache,
depending on the workload read and write I/O characteristics.
Mainframe hosts can specify special attributes (for example, cache fast
write command) to write data (typically sort work data) without write
duplexing. This data is not duplexed and is usually given a discard command
at the end of the sort, so that the data will not be destaged to the drives.
Data Protection
The Virtual Storage Platform is designed so that it cannot lose data or
configuration information from the cache if the power fails. The cache is
protected from data loss up for up to ten minutes by the cache destage
batteries while the data is copied to the cache SSD (flash memory) on the
cache boards. This is explained in detail in Battery backup operations on
page 4-5 .
Shared memory
The Virtual Storage Platform shared memory is not on a separate memory
module as it was in the previous hardware systems. Shared memory resides
by default on the first pair of cache boards in controller chassis #0. When
you install software features such as Copy-on-Write Snapshot or Universal
Replicator, the shared memory usage increases as software features are
installed. Shared memory can use up to 48 GB, which is the maximum
amount of shared memory available if the cache in the first cache board pair
is configured to the maximum of 64 GB.
Depending on how much cache memory is installed, it may be necessary to
install more cache memory as more software features are installed in the
system. Up to 32 GB can be installed on each cache board. When 32 GB of
cache is installed, it is also necessary to install a second SSD (cache flash
memory) on the cache board to back up the cache in case of power failure.
Each SSD is 16 GB.
In addition to cache, the shared memory on each cache board contains a 1/
2 GB cache directory to safeguard write pending data in the cache in the
unlikely case of double failure of the shared memory cache area. The cache
directory has mapping tables for the VSD LDEVs and the allocated cache
slots in each VSD cache partition.