Intel AS/400 RISC Server - Manual (Page 285)

IXS and IXA I/O operations (disk, tape, optical and virtual Ethernet) communications occur through the
individual IXS and IXA IOP resource. This IOP imposes a finite capacity. The IOP processor utilization
may be examined via the iSeries Collection Services utilities.
The performance results presented in the rest of this chapter are based on measurements and
projections using standard IBM benchmarks in a controlled environment. The actual throughput
or performance that any user will experience will vary depending upon considerations such as the
amount of multiprogramming in the user's job stream, the I/O configuration, the storage
configuration, and the workload processed. Therefore, no assurance can be given that an
individual user will achieve throughput or performance improvements equivalent to the ratios
stated here
.
17.3 System i memory rules of thumb for IXS/IXA and iSCSI attached servers.
The i5/OS machine pool memory “rule of thumb” is generally to size the machine pool with at least twice
the active machine pool reserved size. Automatic performance adjustments may alter this according to the
active load characteristics. But, there are base memory requirements needed to support the hardware and
set of adapters used by the i5/OS partition. You can refer to the System i sales manual or Work Load
Estimator for estimates of these base requirements. The “rules of thumb” below estimates the additional
memory required to support iSCSI and IXS/IXA.
17.3.1 IXS and IXA attached servers:
I/O occurs through fixed memory in the machine pool. The IXS and IXA attached servers require
approximately an additional 4MBytes of memory per server in the machine pool.
17.3.2 iSCSI attached servers:
IBM Director Server is required in each i5/OS partition running iSCSI HBA targets. IBM Director
requires a minimum of 500 Mbytes in the base pool.
The specific memory requirements of iSCSI servers vary based on many configuration choices, including
the number of LUNs, number of iSCSI target HBAs, number of NWSDs, etc.
A suggested minimum
memory “rule of thumb” 11 is:
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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Copyright IBM Corp. 2008 Chapter 17 - Integrated BladeCenter and System x Performance 285
11
Based on a rough configuration of 5 LUNS per server, 2 VE connections per server, and two target HBA
connections per server .