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Chapter 10 - Performance Tuning and Troubleshooting
176
VMA-series Memory Array Installation and Service Guide
HP-AM456-9002A Rev 01
Block Size
Consider the block size when testing for maximal bandwidth versus maximal
IOPS. Use a larger block size (megabytes, if necessary) when evaluating
bandwidth performance and smaller block sizes, such as 4kB, when evaluating a
device’s maximum IOPS potential.
Latency
Use
perf_test
to measure round-trip latency of an I/O request. Generally,
latency measurements should only be made using one thread and an
asynchronous I/O depth of one. Any other values skew the latency
measurements.
Direct-Attached and Buffered I/O
Use
perf_test
defaults to use the system buffer cache. In some cases, such
as sequential read tests on systems with a large amount of RAM, this can be an
advantage because data read from the device can be cached in the system’s
buffer cache.
However, that does not help in qualifying the speed of the device itself. To better
qualify the speed of the device being tested, use the
-o
option, which tells
perf_test
to use the
O_DIRECT
flag when attaching to the device, thus
circumventing the buffer cache.
Specify less threads using the
-t
option for Windows and Linux drivers and
specify more asynchronous I/Os using the
-A
option, as it reduces CPU context
switching.
On Linux, the
-o
option is only available if the
libaio
and
libaio-devel
packages were installed with the Violin Utilities installation. For more information
see
Read / Write Ratio
Use the
-r
and
-w
options for defining a read:write ratio.
The default is 100% reads. To specify a 100% write mix, use the
-w1 -r0
options. For a
50%
read/write mix, use
-w1 -r1
.
The
-r
and
-w
values are added together to create a ratio for I/Os. For example,
-r80 -w20
is the same as
-r8 -w2
, which is effectively 80% reads and 20%
writes.
Baselining the Memory Array System
It is recommended that you use the
perf_test
utility to characterize the
Memory Array system as the first step in qualifying the system. These tests
should include:
Содержание VMA Series
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Страница 21: ...PART I Product Overview Chapter 1 VMA series Overview Chapter 2 Violin Intelligent Memory Modules ...
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Страница 180: ...Appendix A Product Models 180 VMA series Memory Array Installation and Service Guide HP AM456 9002A Rev 01 ...
Страница 186: ...Appendix B Compliance Information 186 VMA series Memory Array Installation and Service Guide HP AM456 9002A Rev 01 ...
Страница 208: ...Appendix C Alarm Reference 208 VMA series Memory Array Installation and Service Guide HP AM456 9002A Rev 01 ...
Страница 300: ...Appendix D CLI Reference 300 VMA series Memory Array Installation and Service Guide HP AM456 9002A Rev 01 ...