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Puzzling issue with write speed

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Christopher Tay
Puzzling issue with write speed
on Aug 21, 2009 at 3:57:24 am


I have a puzzling situation which I'd like to share here...perhaps someone has some suggestions.

The storage is a StorNEXT based SAN and there are 3 storage volumes, one is fibre-channel based and the other two are SATA based. Let's call them :

Storage A (FC based)
Storage B (SATA based #1)
Storage C (SATA based #2)

In Storage C volume, when we do a Quicktime export to it, it takes about 3 times longer than exporting to Storage A and B. So for example if we have a 45mins sequence, without any effects applied, exporting to Storage A and B as a reference movie will take about 2mins or so. Exporting to Storage C will take about 6 mins.

If we do the same but export as self-contained, it will take about 22mins on Storage A and B but 1 hour on Storage C and it doesn't matter if the source clip that we're reading from resides in Storage A, B or C.

However I am able to injest 3 x SD PAL uncompressed streams into Storage C (1 x 8bit and 2 x 10bit) without any dropped frames. I am also able to injest 1 x HD PAL 1080i uncompressed stream into Storage C without any dropped frames.

At first we suspect that Storage C might be badly churned but if it is, then it shouldn't be able to sustain the real time video injest without dropping frames.

What is puzzling is that why exporting into Storage C would be 3 times slower than the other two storage volumes.

Any ideas ?


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Bob Zelin
Re: Puzzling issue with write speed
on Aug 21, 2009 at 11:11:29 pm

the very fact that you are saying "one is so much faster than the other" means absolutely nothing. To test performance, you use simple tools, like AJA System Test, or more advanced products like IOMeter (a free download) to test system performance. You can test each drive array on the local computer, and then you can test performance across the network. There is no magic fix for this. You sit there, and one at a time, you test each drive array, and you test each computer, and it's connection speed, using a simple free product like AJA System Test. Once you identify which product is running slow (a specific drive array, or a specific client computer) - you can then test each drive on the "slow" drive array, or look for errors in the network setup menus of the "slow" client computer. Or perhaps you have a defective host adaptor. You determine this by swapping it out with another card from a working computer. Does this take a long time to do all of this - YOU BET IT DOES. That's what we do for a living. Solving problems.

Bob Zelin

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Eric Hansen
Re: Puzzling issue with write speed
on Aug 24, 2009 at 11:50:04 pm

maybe a drive is about to fail. i've had issues like you describe (volumes slow sometimes but not other times) that eventually turned out to be a drive about to fail. a drive in the process of failing will make a controller nuts, which could be what is slowing things down.

is this an issue you've only recently had or has it always been the case with this RAID? does it have the same stripe breadth, sector size, etc, as the other SATA RAID?


Eric Hansen, The Audio Visual Plumber -

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