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The ESS provides fibre-channel connectivity to System/390 host systems with the
IBM 9032 Model 005 ESCON director. The 9032 FICON-bridge option provides
connection and switching among FICON channels and ESCON controllers.
Cache
The ESS provides the following cache features that improve performance:
v 8-GB standard cache and 16-GB optional cache for Models F10 and F20
v 6-GB standard cache for Models E10 and E20
v Fast read from cache
v Asynchronous write
v Least-recently-used (LRU) replacement
v Internal error recovery
Nonvolatile storage
The ESS provides 384 MB of nonvolatile storage (NVS) with all models. Cluster 1
and cluster 2 each have 192 MB of NVS, which enables them to store a second
copy of write data. This ensures data integrity in the event of a power failure.
The NVS for cluster 1 is located in cluster 2; cluster 2 NVS is stored in cluster 1.
Should a cluster fail, the remaining cluster can access the data from the failed
cluster. Battery backup power protects NVS in each cluster.
Concurrent maintenance
The ESS supports concurrent maintenance. Service personnel can replace a failed
component, such as a disk drive module (DDM), without shutting down the entire
system. Your host system continues to access data while service personnel replace
the component in the ESS.
FlashCopy
The FlashCopy feature provides an instant or point-in-time copy of a logical volume.
FlashCopy makes it possible for you to access both the source copies and the
target copies. This enables applications that use either the source copy or target
copy to operate almost without interruption. The source and target volume must
both be within the same logical subsystem.
The ESS supports FlashCopy on System/390 hosts and open system hosts (SCSI
or fibre channel). FlashCopy is not supported on AS/400 host systems. You can
initiate and use FlashCopy from the ESS Web Copy Services interface. See the
IBM Enterprise Storage Server Web Interface User's Guide for more information.
If a volume is reserved by host application software it cannot be used as a target
volume for FlashCopy.
16
ESS Introduction and Planning
The ESS improves performance by using algorithms to store data in cache tracks
that have the greatest probability of access by a read operation.
The ESS provides improved write performance by completing an operation
without accessing DDMs.
The ESS checks tracks at the top of the cache LRU list for updates in cache that
are not on the DDM. The ESS schedules tracks at the top of the nonvolatile
storage LRU list for destaging. The ESS can then allocate the tracks without a
delay during destaging.
The ESS performs error recovery on DDM-to-cache operations.
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