IBM i series Handbook page 502

Operating System/400 (5722-SS1)
• PTF performance improvements: The amount of time required to load and apply
program temporary fixes (PTFs) is reduced. Only program objects and service
program objects that have changed as a result of the PTF are replaced. Objects that
were on the system as a result of a superseded PTF are bypassed.
• Large capacity disk load balancing: The ability to balance data across disk arms in
an ASP, based on performance, is provided in V4R4. The disk load balancing function
identifies hot data versus cold data and spreads data across the disk arms to balance
utilization accordingly. Disk load balancing also provides the ability to balance data
across disk arms in an ASP, based on capacity. Data is spread across arms so each
arm average utilization is the same percentage. This is especially useful when disk
arms are added. The ability to move low access data to slower, high capacity disk
arms within an ASP (for example, compressed disk) is provided as well. This involves
identifying hot versus cold data and moving the cold data to slower disk. Specific data
can also be targeted to move to a slower disk. These functions are controlled with CL
commands (no GUI interface).
• Teraspace storage: Each iSeries job has up to 1 TB of contiguous, process-local,
temporary storage. Applications can allocate dynamic storage in excess of 16 MB
using C dynamic storage functions (malloc, calloc, realloc, and free) and the POSIX
shared memory APIs.
• Expert Cache: Provides a disk cache tuner option, which allows the iSeries server to
take advantage of available main storage capacity. It dynamically responds to system
jobs to cache pages of data in main storage to reduce the time to process disk I/O.
• Auxiliary storage pools (ASPs): Are individual disks reserved for particular objects
(like individual libraries), which can be used to isolate those objects to assist in their
recovery. Up to 15 user ASPs allowed. All systems ship with one system ASP
configured.
• Independent auxiliary storage pool (IASP): New with V5R1, IASP can be defined
that can be moved from one iSeries server to another. User Defined File Systems
(UDFS) can be created in these IASPs. When the IASP is moved from one system to
another, the UDFSs on the IASP can then be mounted on the new system and made
available to applications and users. This protects customers from hardware failures
other than hard disk failures of the IASP.
• Integrated Hardware Disk Compression: Compression of data on disk is supported
by OS/400. Data is dynamically compressed and uncompressed by the DASD
controller as data is written to and read from disk. Disk compression does not effect
the main CPU utilization since this function is performed by the DASD controller IOP.
Integrated Hardware Disk Compression is supported by select DASD controllers.
Compression is limited to user ASPs only. The system ASP cannot be compressed.
Most data compresses at a 20 to 40% reduction. The compression reduction and
subsequent impact on DASD performance depends on the attributes of the data.
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iSeries Handbook