performance test on USB drive

[ottoking]

hello Sir,
the following is the test results of USB drives.
yellow line is RIDATA 2G USB drive.
red line is SanDisk 2G USB drive.
I just can't understand why the line is incised. How to explain that??
Second, on the speed v time graphy, why the RIDATA's line suddenly drop to zero??
http://ottoking.spaces.live.com/?_c1...&_c=PhotoAlbum
http://ottoking.spaces.live.com/?_c1...&_c=PhotoAlbum

[David (PassMark)]

The graph you selected, Instantaneous MB/Sec vs Time, is not smoothed or averaged (There is another averaged graph for that).

The result is that the line appear jagged becuase the sample period can pick up a different number of I/O operations each sample period. To take a simple example, imagine that each sample was 1 second apart. In the 1st second 3 write operations occur. In the 2nd second 4 write operations occur. In the 3rd second 3 write operations occur again, etc...

If each write is 32KB, then the rate for the 1st second is 96KB/Sec and the rate for the 2nd second is 128KB/sec and so on forming a jagged line.

There are probably also other factors at play at reduce the smoothness of the line. e.g. updates to the FAT, which are not included in the data rate.

The rate can fall to 0 for one of the lines on the 'MB/Sec vs MB transfered' graph because the slow device didn't have time to write that much data before the test time expired. The fast device transfered more data.

[ottoking]

now I understand.
thank you every much.