Databases Reference
In-Depth Information
can see that this occurs at about 59MB/Sec, and this is for Sequential access, and you are getting similar
numbers of both Read and Write. Now the IOPS is a little more difficult, as you are getting about the
same MB/Sec, but with different block sizes you get very different IOPS numbers. However this is what
you should expect. The disk is capable of transferring a maximum of 59MB/Sec, and it can either do that
as a lot of small accesses or fewer larger accesses. The limits to this seem to be that you can go down to
16-32K blocks before throughput drops below 58.86MB/Sec, and you can go up to 1024-2048KB before
seeing latency go above 10 mSec.
So, you could reasonably characterize this disk as being capable of 60MB/Sec for 16KB to 2048KB
Sequential Reads and Writes.
Its Random access capabilities are lower. You only got 24.85MB/Sec and 99.40 IOPS at 256 KB block size
for Random Write, and 12.81MB/Sec and 102.50 IOPS at 128 KB block size for Random Read. (However,
the next result for Random read at 21.37MB/Sec and 85.50 IOPS is only at 11 mSec latency, so you might
rerun this test two to three more times and see if you can get that latency to drop, or alternatively use the
higher figure with a caveat that it's just above the acceptable latency limit.)
2DiskTests32KBStripe
The next step was to configure two of the disks into a stripe set and rerun the tests. Following is the table
of results for that set of tests. There were a number of options for setting the stripe size for the array, and
the smallest at 32K was chosen for this test.
Stripe Size
The Stripe Size is the amount of data written to each disk in the stripe set before a write
moves on to the next disk in the set. For writes smaller than the stripe size, the write
will only go to one disk, provided the write is aligned. For more on disk alignment, see
Chapter 6.
For writes larger than the stripe size, the write will go to (write size/stripe size) disks.
The benefit of this is that you can now write to more than one disk at the same time,
thus increasing the throughput to the disk.
Table 12-7: Two-Disk Test E Results
Read/Write
Sequential/Random
Block Size
IOPS
MB/Sec
Avg Latency
W
random
8
495.9
3.87
1
W
random
16
412.2
6.44
1
W
random
32
311.7
9.74
2
W
random
64
285
17.81
2
W
random
128
198.4
24.8
4
Continued
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