hIOmon SSD Performance Monitor - Understanding desktop usage patterns.

[Ao1]

Thanks alfaunits. Edit:The last entry on the excel sheet is a jpeg and the read data transfer size is exactly the same file size as the jpeg. When I say read ahead what I mean is that the act of hovering the mouse over the file was enough for Windows to read the data from the device in advance of the file actually being executed. Am I seeing that incorrectly?

I'm still struggling to understand the process of a large file transfer.

At a best guess.....

A large file is constructed from multiple file sections that are linked by records that allow contiguous reading. On a HDD these files are placed close together to minimise access time. Over time they may become fragmented, which slows down the read time. On an SSD sections of the file are placed randomly and are moved around for wear levelling. To read the file the SSD therefore needs to locate all the file records related to the file, which are distributed randomly over the SSD.

To speed up this process NCQ enables up to 32 commands, which can be executed in parallel. I'm assuming that this is why in post #137 (with NCQ enabled) that the read time was the same for a large file and multiple (unlinked) smaller files. In other words contiguous reading was enabled by commands being executed in parallel rather than serially as in the case of HDD. The net result is that latency between reads is reduced. Edit: the benifit of NCQ is not therfore limited to higher qd's.

If the maximum read transfer size is 104,8576 I'm assuming that one IOP count is required to read that portion of data. If the same size section of data is read multiple times the read IOP count is multiplied and the combined read transfer length equals the sum of the read IOP count multiplied by the size of the data blocks being transferred.

Based on the above I'm assuming that larger files have larger and more consistent read transfer sizes, so the IOP count is less for a large sequential transfer when compared to multiple small files. I.E. the average of the transfer size block is much larger than say a smaller file transfer.

This however does not seem to not be the case with the AVI file transfer. Presumably the read format structure is the same, yet with NCQ the read IOP count is considerably higher to read the same amount and format structure of data.

Now I'm stuck. I can't understand why that would be the case.