IBM System Storage DS3500 Introduction And Implementation Manual page 280

7914Admin_Logical.fm
– RAID 1 or RAID 10=Number of drives / 2
– RAID 5= Number of drives - 1
– RAID 6= Number of drives - 2
If the resulting Segment Size is >512 KB, then divide it by an integer number staring with 2
to obtain multiple data stripes of each block requested.
Tips: The possible segment sizes available are 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, 256
KB, and 512 KB.
Storage Manager sets a default block size of 128 KB for every logical volume, except for
RAID3 volumes, which are set to 256 KB.
For database applications, block sizes between 32–128 KB have shown to be more
effective.
In a large file environment, such as media streaming or CAD, 128 KB or more are
recommended.
For a Web server or file and print server, the range should be between 16–64 KB.
The performance monitor can be used to evaluate how a given segment size affects the
workload.
Note: A performance testing schedule should be undertaken in the environment before
going into production with a given segment size. Segment size can be dynamically
changed, but only by rewriting the data, which consumes bandwidth and impacts
performance. Plan this configuration carefully to avoid having to reconfigure the options
chosen.
To initiate segment size change, follow these steps:
1. Highlight the logical drive in the Logical pane tree and right click to select Change 
Segment Size  value. The value highlighted in menu is just a double of current value, or
a half of current value. See example in Figure 9-32.
Figure 9-32 Change Segment Size menu
2. If you select required new segment size, a warning window shown in Figure 9-33 on
page 257 opens.
256
IBM System Storage DS3500: Introduction and Implementation Guide
Draft Document for Review March 28, 2011 12:24 pm