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D a t a D i r e c t N e t w o r k s S 2 A 9 5 5 0 U s e r G u i d e
M a n a g i n g t h e S 2 A 9 5 5 0
3.3 Performance Management
The S2A9550 offers great flexibility in optimizing performance with extensive monitoring and
reporting capability.
3.3.1 Optimization of I/O Request Patterns
The S2A9550 manages the pre-fetch and cache efficiency by LUN.
3.3.1.1 Display Current Cache Settings
The
CACHE
command displays the current cache settings for each LUN in the system
(Figure 3-29)
.
You can use the
LUN=x
option to specify which LUN to change. If no LUN is specified, changes will
be applied to all the LUNs by default. Valid LUN’s are 0 to 127. Default is to apply to all LUNs.
3.3.1.2 Cache Segment Size
System performance can be optimized by changing the cache segment size to match the size of the
host I/O requests. A large cache segment size may give better performance for large I/O requests and
a small cache segment size may give better performance for small I/O requests. For the best
performance, the cache segment size should be larger than the average host I/O request size. You may
use the
STATS LENGTH
command to determine the average host I/O request size. The cache segment
size should not be changed during heavy I/O conditions because the system will temporarily halt all
I/O requests while the changes are taking effect.
Use the CACHE SIZE=x command to set the cache segment size for the specified LUN in KBytes. Valid
segment sizes are 64, 128, 256, 512, 1024 and 2048. The default value is 128. This command should
not be issued under heavy I/O conditions because the system will momentarily halt all I/O requests
while the changes are taking effect.
3.3.1.3 Writeback Cache Settings
Writeback caching allows the system to increase the performance of handling write I/O requests by
storing the data in cache and saving the data to the disks at a later time.
Use the CACHE WRITEBACK=ON|OFF command to enable/disable writeback caching for the
specified LUN. Default setting is ON.
The
CACHE WRITELIMIT=x
command specifies the maximum percentage of the cache that can be
used for writeback caching. The system will force all writeback requests to be flushed to the disks
immediately if the percentage of writeback data in the cache exceeds this value. Valid range is 0 to
100. Default value is 75.
Current Cache Settings
Maximum
Prefetch LUN
Write
Caching
On
------------------------------------------------------------------------
x1 Enabled 0
Figure 3-29 Current Cache Settings Screen
S2A [1]: cache
high
640.0 Mbytes of Cache Installed
MF
Bit
Prefetch
Ceiling
Read
Priority
Write
Priority
65535 high
On x1 Enabled 1 high 65535 high
On x1 Enabled 2 high 65535 high
On x1 Enabled 3 high 65535 high
(4096 Segments of 128 Kbytes)
writeback limit: 75%