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External RAID Playback Hiccups

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Dan Quintero
External RAID Playback Hiccups
on Nov 8, 2011 at 1:44:54 am

Any reason a quicktime would skip/hiccup on one RAID and play back fine on another?

The quicktime/s are roughly 30 mins each and they're DVCPRO HD 1080p30. The file/s jump and skip about every 5 mins on the Qx2 but they playback fine on the Lacie. I've hooked the Qx2 up to different machines and I get the same results. It skips whether I hook it up via FW800 or eSata. Ruled out conflicting RAID controllers (we have a caldigit HDOne) because it skips on computers without any eSata/RAID controllers. When the playback skips the activity monitor will show a dip and spike in the data read. It'll read at a pretty constant 15MB/s and then dip and spike to somewhere around 25MB/s. It doesn't do that when you're playing it back on the Lacie. xbench, quickbench, and blackmagic's speed test all show the Qx2 as being fast and what-not. This is our third 12TB Qx2. We sent the first one in for replacement after the enclosure wouldn't stop beeping (it also skipped on playback with the same files as a RAID5) and this is the one they sent back. We recently got another one, setup as RAID0, with the idea that wed be able to edit ProResHQ/DNxHD 175x via eSata. We haven't started editing on the 3rd one, but I'm assuming we're going to have the same issues.

Any ideas?

Specs:
MacPro, 2x2.66GHz Quad, 8GB Mem
Decklink Studio
Other World Computing's 12TB Mercury Pro Qx2, RAID0
Lacie's 4TB 4Big Quad, RAID0
Hooked up via FW800 or eSata

Go fly fishing.


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Steve Modica
Re: External RAID Playback Hiccups
on Nov 8, 2011 at 4:13:39 pm

one of the nice things about OS X is Dtrace. You can run various Dtrace scripts to see what's going on.
iosnoop is one such dtrace script. With -D it will show you all of the IO going through the system and the latency associated with each. We use that to evaluate storage solutions and determine whether they can sustain video streams. Most can't.

Steve Modica
CTO, Small Tree Communications


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Dan Quintero
Re: External RAID Playback Hiccups
on Nov 8, 2011 at 9:39:14 pm

Thanks for the response. I've never used DTrace, but I'll give it a shot. From my experience, I've never had a drive/RAID not be able to sustain a DVCPROHD 1080p30 (~15MB/s) stream. Even a LaCie rugged drive (5400rpm) can stream DVCPROHD via FW800 without lagging/skipping. From everything I've read, these Qx2 drives should be able to play back a DVCPROHD file. Any other ideas?

Go fly fishing.


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