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Chapter 10 - Performance Tuning and Troubleshooting
176
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
to measure round-trip latency of an I/O request. Generally,
perf_test
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
defaults to use the system buffer cache. In some cases, such
perf_test
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
to use the
perf_test
circumventing the buffer cache.
Specify less threads using the
specify more asynchronous I/Os using the
switching.
On Linux, the
option is only available if the
-o
packages were installed with the Violin Utilities installation. For more information
see
Libaio Development Package
Read / Write Ratio
Use the
and
options for defining a read:write ratio.
-r
-w
The default is 100% reads. To specify a 100% write mix, use the
options. For a
read/write mix, use
50%
The
and
values are added together to create a ratio for I/Os. For example,
-r
-w
is the same as
-r80 -w20
writes.
Baselining the Memory Array System
It is recommended that you use the
Memory Array system as the first step in qualifying the system. These tests
should include:
VMA-series Memory Array Installation and Service Guide
flag when attaching to the device, thus
O_DIRECT
option for Windows and Linux drivers and
-t
option, as it reduces CPU context
-A
libaio
on page 120.
-w1 -r1
, which is effectively 80% reads and 20%
-r8 -w2
perf_test
option, which tells
-o
and
libaio-devel
-w1 -r0
.
utility to characterize the
HP-AM456-9002A Rev 01
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