HP VMA-series Memory Arrays Manual do Utilizador descarregar pdf (Página 176)

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 Libaio Development Package on page 120.

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:

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