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Update Tue, 25 Feb 2014 00:21:06 -0800: added "Effects of Write-Caching" section.
Update Tue, 25 Feb 2014 13:12:01 -0800: added "Larger Writes" section.
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Each drive seems to behave differently. For the 530, write-caching seems to have no effect on rcmonster but improves latency for one-byte writes by a factor of six on rc66 and flygecko. This opens up a lot of questions... See also Larger Writes section below.
Larger Writes
Many people have suggested that writing 1 byte is not efficient and writing more bytes should be faster. I tried it both with write-caching on and off using the same string of random a-z characters for each write.
| host | disk | write-caching | 1 byte | 1024 bytes | 4096 bytes | 8192 bytes |
|---|---|---|---|---|---|---|
| rcmonster | 520 | on | 440us | 570us | 1.0ms | 1.0ms |
| rcmonster | 530 | on | 9.7ms | 12.0ms | 19.6ms | 19.8ms |
| rc66 | M4 | on | 3.7ms | 5.1ms | 9.2ms | 10.4ms |
| rc66 | 530 | on | 9.8ms | 12.5ms | 21.0ms | 21.2ms |
| flygecko | X25-M | on | 210us | 370us | 910us | 950us |
| flygecko | 530 | on | 9.7ms | 12.1ms | 19.6ms | 19.7ms |
| rcmonster | 520 | off | 100us | 160us | 400us | 420us |
| rcmonster | 530 | off | 10.5ms | 17.5ms | 55.9ms | 68.9ms |
| rc66 | M4 | off | 1.5ms | 2.6ms | 5.6ms | 7.2ms |
| rc66 | 530 | off | 1.9ms | 3.0ms | 6.9ms | 8.6ms |
| flygecko | X25-M | off | 1.0ms | 1.7ms | 3.5ms | 3.7ms |
| flygecko | 530 | off | 1.7ms | 2.4ms | 4.9ms | 5.0ms |
In these tests, no drive is faster at writing more than 1 byte than it is at writing 1 byte. Most drives take about 2-4x as long to write 8KB as they do to write 1 byte.