Multiple Hard Drive Testing

[Joec]

Hi.
I'm looking at setting up a system which will be used to test a number of ATA133 EIDE 250MB Western Digital Hard drives.
The BIT software has been recommended, to do a test of the full drive capacity using the High Low frequency data overwrite pattern. What drive characteristic does this pattern test?
Ideally the system should be capable of running as many drives at one time as possible to maximise the output. If the total test time must be lower than 20 hrs is it possible to estimate the quantity of drives which could be tested in this manner by one PC system ?
Other than the drive response, what would be the primary limiting factors on the speed of testing possible, PC CPU speed, Ram size, the controller which implements EIDE channel, Operating System ..etc?
By adding additional drives to the system will this cause a linear reduction in the testing speed for each drive added?
Is there an optimal number of drives which would give best return for time spent testing?
Would the organisation of the drives in OS, or on EIDE channels (Primary V Secondary) have any effect on speed?
Thanks in advance

[David (PassMark)]

The High Low frequency data overwrite works by first writing a file with a high frequency pattern (10101010101010010101…), then overwriting this with a low frequency pattern (00001000010000100001…) and then verifying that the low frequency pattern has been fully and correctly written. So the disk will do two writes and one read for each byte. Obviously the 2nd write should overwrite the first write. This is not the quickest option as 2 times the writing is done.

Up to 20 hard drives can be tested at the same time. (in this sense, a hard drive might include an entire RAID array and other types of drives like USB key drives).

Clearly however most PC's will not have the bus speed nor the CPU power to run 20 drives, at full speed, at the same time.

On a P4 2.8Ghz with hyperthreading, with a single hard drive, and 100% duty cycle (maximum speed) we get about 6% CPU usage during writing and 38% CPU usage during reading. (The CPU needs to verify the data, so more use is made of the CPU during reading than writing).

When we add a 2nd physical drive the CPU usage about doubles. 12% when both drives are writing and 75% when both drives are reading (at maximum speed).

So if you assume the drives will drift out of synch (some are reading while others are writing) then I think 4 drives would be about the limit for a typical PC. BurnInTest will work with more but the throughput will start to drop.

You would need to do some measurements on your own PC, with your own device drivers and hard drives to really know what is the optimal level.

Maybe you can test more drives at a time, by putting the drives into a RAID array?

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David