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RAID configuration for dual 16-bay SAS expanders

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Antoine Durr
RAID configuration for dual 16-bay SAS expanders
on Dec 14, 2011 at 8:09:31 pm

Hi,

I'm looking to set up a Mac based workstation to run Scratch. I was originally planning on getting a pair of iStoragePro16's, each hooked up to one of the two ports of an ATTO R680 (or possibly on one port each of two separate R680's). My plan was to RAID6 them, and since all the work I do is in stereo, essentially have one expander for each eye.

However, knowing a bit more about Scratch now than I did 2 months ago, having the left eye frames on one device and the right eye frames on another requires quite a bit more file management. Data from on-set doesn't come nicely separated by eye, and it's a lot cleaner to have an exact duplicate of what they have (source is .R3D and .cine files).

So my question: should I daisy chain the two chassis? Or run them as RAID 60? (Not sure if it's 60 or 06, basically stripe the two chassis, each of which itself is RAID6). Or some other configuration entirely? The bandwidth isn't to handle the .R3D's or .cine's, per se, but to handle stereo 4K DPX files as fast as possible (I know I won't get 24fps on stereo 4K, but if I can get 12fps, that's pretty decent -- I'm mostly doing conforms and other offline stuff, not online DI work).

Thanks!

-- Antoine


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Bob Zelin
Re: RAID configuration for dual 16-bay SAS expanders
on Dec 16, 2011 at 2:34:32 am

a single configuration (one 16 bay) from what you describe above will give you 1600 MB/sec read speed. I HATE when Assimilate relates drive speed to "number of frames per second". This means absolutely NOTHING in the disk drive industry. You have to show DATA rate, not frames per second that you can achieve.

If you do a RAID 60, or try to create a RAID 6 with 32 drives (I never tried to do this), you will get better speeds, but of course, more risk for failure.

You should call up Assimilate (Nacho ? ) and say "what the hell is wrong with you - give me a DATA RATE REQUIEMENT for this, and not this Frames/Sec. specification. No drive manufacturer can answer this question, as Assimilate is not an industry standard, and no one is going to spec out a drive array based on performance from Assimilate Scratch.

Bob Zelin



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Antoine Durr
Re: RAID configuration for dual 16-bay SAS expanders
on Dec 16, 2011 at 5:16:11 am

The data rate quoted is 1800 MB/sec to run a single stream of 4k DPX files, so a single 16-drive chassis like this will not achieve a smooth running 24fps. I'm not sure if the 1800MB/sec includes some pad, as the raw data rate of 4K DPX files is just below 1200 MB/sec.

And some of the work I do is 30fps planetarium material, which is 4k x 4k, so that's probably in the 2300 MB/sec range, per eye!

I will be working on 2K proxies of the 4K material. The 2K's will run in realtime. And if I run 4K's, they'll just run slower than realtime.

What are the dangers of running a RAID 60 setup? Is a RAID60 more "hazardous" than a dual RAID6 setup?


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Bob Zelin
Re: RAID configuration for dual 16-bay SAS expanders
on Dec 16, 2011 at 8:11:29 pm

the danger is that everything fails, and if you span two chassis together for extra speed, and one chassis fails, you lose everything.

I have seen this happen with XSAN arrays. One volume that is part of a spanned group goes down, and you are screwed.

Who ever said that "state of the art" was easy.

Bob Zelin



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