Performance

 

Workload

Tools Reports

 

description

Workload

 

Workload

statistics

characteristics

Other

 

 

requirements:

 

 

HA, DR etc.

 

 

 

Rules of thumb

 

SAN Fabric

 

 

 

Proposed

 

 

configuration

 

Workload from

 

 

other servers

 

 

 

Modeling with

Adjust config

 

Disk Magic

 

based on DM

 

 

 

 

modeling

Requirements and

 

expectations met ?

No

 

 

 

Yes

 

 

Finish

 

Figure B-34 Process for sizing external storage

Planning for arrays and DDMs

In general, although it is possible to use 146 GB and 300 GB 10K RPM DDMs, we recommend that you use 73 GB 15K RPM DDMs for iSeries production workloads. The larger, slower drives may be suitable for less I/O intensive work, or for those workloads which do not require critical response times (for example, archived data or data which is high in volume but low in use such as scanned images).

For workloads with critical response times, you may not want to use all the capacity in an array. For 73 GB DDMs you may plan to use about 300 GB capacity per 8 drive array. The remaining capacity could possibly be used for infrequently accessed data. For example, you may have archive data, or some data such as images, which is not accessed regularly, or perhaps FlashCopy target volumes which could use this capacity, but not impact on the I/O per sec on those arrays.

For very high write environments, you may also consider using RAID-10, which offers a higher I/O rate per GB than RAID-5 as shown in Figure B-3 on page 356. However, the majority of iSeries workloads do not require this.

Cache

In general, iSeries workloads do not benefit from large cache. Since there is no choice for cache size on DS6000, you should ensure that your workload is not excessively cache-friendly. This can be seen in OS/400 Performance Tools System, Component and Resource Interval reports. However, in general, with large iSeries main memory sizes, OS/400 Expert Cache can reduce the benefit of external cache.

354DS6000 Series: Concepts and Architecture

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IBM DS6000 Series manual Planning for arrays and DDMs, Cache