122 IBM Midrange System Storage Hardware Guide
4.1.6 Cache parameters
Cache memory is an area of temporary volatile storage (RAM) on the controller that has a
faster access time than the drive media. This cache memory is shared for read and write
operations.
Efficient use of the RAID controller cache is essential for good performance of the DS5000
storage subsystem.
Figure 4-8 shows a schematic model of the major elements of a disk storage system, which
are elements through which data moves (as opposed to other elements, such as power
supplies). In the model, these elements are organized into eight vertical layers: four layers of
electronic components shown inside the dotted ovals and four layers of paths (that is, wires)
connecting adjacent layers of components to each other. Starting at the top in this model,
there are some number of host servers (not shown) that connect (over some number of
paths) to host adapters. The host adapters connect to cache components. The cache
components, in turn, connect to disk adapters that, in turn, connect to disk drives.
Figure 4-8 Conceptual model of disk caching
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.
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
paths to hosts
1...n
1...n
1...n
1...n
1...n
1...n
1...n
1...n
paths to cache
paths to adapters
paths to disks
host adapters
cache
disk adapters
disk drives
To Next Page
Loading...
Need help?
General