Intel Server RAID Q1 2009 boot camp training lab workbook

Q1 2009 Intel
®
Server RAID Boot Camp Training
B: Comparing sequential and random performance
Sequential performance and random performance are two different characteristics of a storage
subsystem. The difference comes from the mechanical nature of HDDs. Both characteristics are
important. Some applications may require higher sequential performance, other applications may
require higher random performance, and some applications may require both.
Sequential performance is measured in Megabytes per second (MB/s)
and represents the amount of
data that can be read (or written) per second from a RAID logical disk as a continuous stream of
consecutive data blocks. Sequential access usually means that HDD heads do not have to move
between the tracks in order to get to the next portion of data. Therefore, there are no huge delays
associated with moving heads. The maximum performance in terms of MB/s can be achieved only
when accessing data sequentially. (HDD heads still have to move to the next track each time the
end of a track is reached, but this movement is negligible compared to movements across hundreds
of tracks.)
Random performance is measured in Input/Output operations per second (IOPS)
. Random
performance is a measure of number of data blocks randomly distributed across the drive can be
read (or written) from the drive per second. Random access means that drive heads have to move to
another location every time in order to get to the next data block.
A common mistake is measuring performance in MB/s while using random or
mixed access pattern.
1. Measure sequential performance
a.
Open iometer.icf file located on the desktop. This file has IOmeter settings configured for this
lab.
b. On the Access Specification tab, select 64KB Sequential Read specification and click Add.
c. Click the Results Display tab, then click the Green Flag button to start the test and wait for
10 seconds for the test to complete.
d. Write down Total I/Os per Second result into the IOPS column in the table below.
e. Write down Total MBs per Second result into the MB/s column in the table below.
2. Measure Random Read Performance
a. On the Access Specification tab, remove 64KB Sequential Read and add 64KB Random Read
instead.
b. Click the Results Display tab, then click the Green Flag button to start the test and wait for
10 seconds for the test to complete.
c. Record the Total I/Os per Second result into the IOPS column in the table below.
d. Record the Total MBs per Second result into the MB/s column in the table below.
3. Compare the results
IOPS MB/s
64 KB Sequential Read _________ IOPS _________ MB/s
64 KB Random Read
_________ IOPS _________ MB/s
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