Ideal Block Size for Sata Raid

[Michael Garber]

Hi Rennie,

I have been trying to figure out the same thing – I have an 8-drive set. I found this post on Apple’s discussion board. Perhaps it can help.

https://discussions.apple.com/message.jspa?messageID=1923502

Regards,
Michael Garber
5th Wall
http://www.5thwallentertainment.com

[Rennie Klymyk]

Thanks for the link Richard. It is definately in the right catagory although it started out in plain english but digressed to some other langauge half way through. I think it’s some form of mathmatical lingo or something. I was thinking along the same lines though, use the AJA data rate calculator but I don’t understand how that relates to the block size. The rate calculator tells me the data rate of the format I’m using, (I’ve used 720X486 10-bit as that would be my highest resolution I would need). I get just under 28 MBYTES/Sec. but I don’t understand how this relates to the way the data is written to the disc. This is about 1 MByte per frame of video so you can’t even get a whole frame on a block on the hard disc. There must be some other form of logic involved with selecting the block size. It makes sense to me to let the heads write in long bursts once it has touched down on the platter as there is always a long stream of relative data to write with video. With smaller block sizes the head has to skip around more times. Perhaps with word proccessing apps. etc. the small blocks are better as data may not fill a 32K block, say for example a simple period . With video streams we are piling on the data thick and heavy pretty much non stop and can fill large block spaces to capacity very easily. By this logic we should be using 512K blocks but then What the Bleep Do I Know!!! The folks in the other thread are kinda stuck on 128K and I’m thinking I’m going to go halfway inbetween on this to 64K till I learn more about this.

“everything is broken”

[Rennie Klymyk]

I just googled an interesting thread, a couple years old but these guys seem to have a lot of bytes in their blocks!

more info.

“everything is broken”

[Kent Kajino]

I was under the impression that one should use large block sizes for large files, such as video files, and small block sizes for small files, such as documents.

If your files size is only 12k, it makes no sense to block off a whole 512k, wasting the unused 500k.

but if you have a 2mb file, then the hard drive records it in just four 512kb chunks, rather than twenty 32kb chunks, so that it doesn’t have to search as hard.

[Rennie Klymyk]

I was scrounging around on the Seagate site and noticed the 15,000 rpm baracuda uses 512 size blocks. They recomend making adjustments in 4,s. Ezample: 512, 516, 520, 524 etc. Those are a lot bigger than anything I’ve heard of so far. I guess when the platter is spinning that fast the heads cover a lot of ground when they touch down. This seems to enforce the logic that video is big stuff and can utilize larger blocks for optimum efficiency.

“everything is broken”