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Performance in Intel IOMeter

Random Read/Write

As I promised above, I’m going to discuss the drives’ speeds at processing random read/write requests at more length now.

At first I showed you how the new Raptor reacts to random requests the size of a sector, i.e. 512 bytes. But what if the data block is larger? We may see some anomaly or, if there is none, we just get the dependence of the random read/write speed on the size of the data block. The drives may even end up doing linear reading.

So, there’s a lot of thinking matter again. These three hard disk drives are manufactured by the same company, yet how different they are! The read-ahead policy of the WD740GD-FLA1 seems to be very conservative in the sense that it doesn’t seem to be trying to read anything in advance. The two WD740GD drives have identical platters, so the difference in their random read speeds can only be explained by different read-ahead algorithms.

The WD1500AHFD seems to be inclined towards look-ahead reading as is indicated by the small performance loss on medium-size data blocks.

And now let’s see what we have at random writing.

And here’s a surprise to you: the WD740GD drives are faster at processing 1 to 32KB data blocks than at processing blocks the size of a sector (512 bytes). It looks like deferred writing doesn’t work for 512-byte blocks or works very lazily (not the maximum number of cache segments is created – perhaps in an attempt to save some cache space?)

A general observation from the two diagrams above is like follows: random reading/writing does not transform into linear operations even when 32MB data blocks are processed.

For linear operations – proceed to the next section!

 
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