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Most efficient use of 2 raid arrays/2 seperate HDs

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August 24, 2010 8:19:36 AM

Hey all,

So as a Blu-ray author by profession, I have been pondering this question a lot. Our machines at work have hard drives laid out as such:

C: = 1 hard drive for OS and programs
Y: = 2 hard drives in RAID 0
Z: = 2 hard drives in RAID 0

Both Y and Z have identical hard drives for their RAIDs, and both are connected through a PCI (possibly PCI-express) RAID controller. 'Drive' from on on refers to the Y and Z RAID arrays. My question is whether it is faster and more efficient to edit data mostly on one drive, or keep going back and forth between drives?

For instance, often we run 40GB .img files through tools that edit some aspect of it, and just output another edited 40GB .img file, so we are talking about pure sustained hard drive performance. Would it be faster to have the source .img file reading from the Y: and writing the output to the Z:, as opposed to having the source and the output on the same drive? The rest of the system should be up to speed, 3.33 xeon dual core cpu but the tools we run aren't programmed for multi-core usage.

My gut tells me that it may be better for this particular system to read and write to different drives, so that you would have both physical discs of the Y drives reading, and both of the Z drives discs writing. However, for non-RAID hard drive systems, where Y and Z were single discs, would the same hold true? I feel like the OS and hard drive logic boards might know you are writing to the same single physical disc, and so might not even send it to the controller, and instead just copy it internally quickly.
August 24, 2010 8:52:10 AM

Its quite simple and logical.
Each drives has a Read/Write speed cap called bandwidth also think it like this the head moves to read the head moves to write so reading and writing to the same drive is a killer for performance as the head has to move to the read area then move to the write area constantly, using 2 different drives the head has to only write and the other one to only read this creates a steady flow of information with no interruption meaning faster transfer rates.

In your case best case scenario is to read from one array and write to the other the only case where its faster meaning the only operation in which u would want to use the same drive and the same partition is if you Move a folder using CUT instead of copying the data again and deleting the old one it will just change the partition table entries the data stays physically in the same place and takes only seconds instead of minutes/hours, but this is just reordering folder structure.
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August 24, 2010 7:38:19 PM

These graphs say a LOT:




Can you provide us with the full specs for all HDDs installed in that system?


MRFS
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a b G Storage
August 24, 2010 7:42:57 PM

p.s. Also, the specs for your RAID controller are also pivotal e.g.
the legacy PCI bus can only be used by one device at a time.

Thus, if your RAID controller plugs into a legacy PCI slot,
is it is very limited by the bandwidth of that bus (~133 MB/second)
and the lack of parallelism.

The legacy PCI bus transmits 32 bits @ 33 MHz = 1,056 Mbps / 8 = ~133 MBps.


MRFS
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