IBM DS6000 Series ユーザーズマニュアル

DS6000 Series: Concepts and Architecture

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.

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.

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