IBM AS/400e User Handbook Manual page 83

This "banding" of data is accounted for in the Extended Adaptive Cache design. The goal is to
cache bands characterized as read or write and read-only. A band that is characterized as
write-only, while cached in the storage subsystem write cache, remains largely unaffected by
Extended Adaptive Cache. Extended Adaptive Cache is designed to not harm the
performance of large blocks of data that are either sequentially written or sequentially read. In
this case, the pre-fetch capability of the disks, as well as other caches in the system, ensures
a quick response time.
Use of Extended Adaptive Cache improves the performance of database-read actions and all
read actions. This includes read actions that are generated by other system components
such as the Integrated Netfinity Server. It also works effectively in storage subsystems that
have Device Parity Protection or mirroring.
Extended Adaptive Cache Restrictions and Considerations
• A #2748/#4748 PCI RAID Disk Unit Controller feature and a #4331/#6831 (CCIN
6731) Read Cache Device is required for functionality. Extended Adaptive Cache is
automatically enabled when these features are installed. There is no user-controlled
on or off switch. The #4331/#6831 Read Cache Device (RCD) is a solid state disk
optimized for use as Extended Adaptive Cache memory and may be added without
system interruption through Device Concurrent Maintenance. There is a maximum of
one cache per controller.
• The RCD occupies in an internal disk slot and works with all other disk types and
capacities.
• Using Extended Adaptive Cache places no restrictions on the use of Device Parity
Protection and mirroring for other disks under the I/O adapter. Extended Adaptive
Cache cannot be used in conjunction with Integrated Hardware Disk Compression on
the same I/O adapter.
• All data in the Extended Adaptive Cache is also on the disks. Therefore, in the unlikely
event of a #4331/#6831 Read Cache Device failure, there will be no data loss.
• A significant decrease in I/O response time and increase in system I/O throughput can
be achieved in most environments. Up to a 50% performance improvement can be
gained, depending on configuration and workload.
• Extended Adaptive Cache is designed specifically to complement AS/400e Expert
Cache and may be used with or without it.
• Extended Adaptive Cache is not considered a pre-fetch type of cache. Therefore, it
does not interfere with the read-ahead capabilities in the disk.
Planning for Extended Adaptive Cache
As is the general case with caches, the system configuration and workload influence the
effectiveness of Extended Adaptive Cache. Extended Adaptive Cache, functioning at the
AS/400e Advanced Technology
AS/400e Advanced Technology
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