IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 2. Hardware configuration planning 33

.

Figure 2-11 Read intensive - 15K rpm versus 10K rpm drives

Figure 2-11 illustrates the example when a read intensive workload was run on both the 10K

rpm and the 15K rpm configurations. The 15K rpm configuration performs better, always

delivering lower response times for all throughputs as compared to the 10K rpm configuration.

You can appreciate comparing the results in Figure 2-10 on page 32 and Figure 2-11, that

when running a higher cache hit ratio workload, the performance gain is less significant, than

when running the lower cache hit ratio workload.

For more detailed estimation, see 4.1, “Disk Magic” on page 86 and Chapter 12,

“Understanding your workload” on page 407.

2.8 RAID implementation

In this section we describe the characteristics of the RAID implementation in the DS6000.

The performance considerations regarding the possible RAID configurations are discussed in

detail later in Chapter 3, “Logical configuration planning” on page 53.

2.8.1 RAID Arrays

The basic unit where data is stored in the DS6000 is the disk drive module (also referred to as

a DDM). Disk drives for the DS6000 are available in capacities of 73 GB, 146 GB, 300 GB

(capacity and speed), and are grouped together in an

four-pack, and these four-packs can be

installed in each on the FC-AL loops. One FC-AL loop can hold up to 16 four-packs, which

means that the maximum number of 64 DDMs can be found in a loop. The

raw or physical

capacity

installed on a loop will depend on the four-packs (their capacity) that are installed on

that loop. Physical capacity is discussed in 2.6.3, “Disk four-pack capacity” on page 27.

Logically, four DDMs are grouped in an

Array Site automatically. As illustrated in Figure 2-12,

initially four DDMs of four 4-packs (16 DDMs) are randomly selected and make up the

Array

Site

. After initial setup, the next Array Site is configured by adding more four-pack DDMs.

Note: These results are just from the simulation of Disk Magic, your performance may

change according to your environment.

Read intensive workload

0

2

4

6

8

10

12

14

16

18

20

0 200040006000800010000

Throughput(IOPS)

response time(ms)

146GB10K Resp time

146GB15K Resp time

read:write=7:3

cache hit ratio=28%

I/O block size=4kB

write efficiency=33%