IBM eserver i5 Handbook page 574

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IASPs. When the IASP is moved from one system to another, 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.
Note: All I/O, not just the disk in the I/O tower, is switched. Any LAN, wide
area network (WAN), workstation controllers, etc. in the I/O tower are
switched at the same time.
Large capacity disk load balancing
The ability to balance data across disk arms in an ASP, based on
performance, capacity, average utilization, and hot and cold data is provided.
i5/OS V5R3 supports an optimization of "Availability" (in addition to Balance,
Performance, and Capacity).
A parity set optimized for availability offers a greater level of protection
because it allows a parity set to remain functional in the event of a SCSI bus
failure. The availability optimization value ensures that a parity set is formed
from at least three disk units of equal capacity each attached to a separate
bus on the input/output adapter (IOA). For example, if an I/O adapter had 15
disk units and was optimized for availability, the result may be five parity sets
with three disk units each attached to separate SCSI buses on the adapter.
i5/OS V5R3 is required to optimize for availability.
These functions are controlled with CL commands.
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 POSIX
shared memory APIs.
Expert Cache
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.
Integrated hardware disk compression
The compression of data on disk is supported by i5/OS and OS/400. Data is
dynamically compressed and uncompressed by the direct access storage
device (DASD) controller as data is written to and read from disk. Disk
compression does not affect the main CPU utilization since this function is
performed by the DASD controller input/output processor (IOP). Integrated
Hardware Disk Compression is supported by select DASD controllers.
IBM Eserver i5 and iSeries System Handbook
540
Draft Document for Review October 18, 2004