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Topic: GDC SX3000 - movie freezing randomly
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-06-2018 01:35 AM
I think I've explained the behavior of Joe Average's RAID here before.
The problem we're facing is that the RAID systems being used in cinema playout servers are "simple" office RAID systems. They target on data reliability rather than guaranteed performance.
If you want to open that Word document from your network drive, you mostly don't care that you need to wait a second or two extra for it to open. It's more important it's still there.
So, a normal RAID system, if one of the disks encounters a reading or writing problem, it will retry to read or write that same block from the disk a few times, every time with a slight delay in between. In many cases, a failing disk will still comply and the RAID array will not push the disk out of the RAID. Only if it triggers a pretty high threshold, the RAID array will finally decide to dump the offending disk. But for any real-time application, some negative impact will already have occurred by then.
The reason why this is designed this way is easy to explain: Reliability. You don't want your office RAID array to drop disks too easily, or you may end up with a broken array pretty quickly and gone is all your data on top of it.
Now, for real-time applications, that rely on a constant performance from a storage array, those average RAID systems are, if we're being honest, not good enough. There are solutions for this: Many enterprise RAID storage arrays can be configured to ensure a constant throughput. But those systems are pretty expensive and therefore not being used in current cinema playout hardware...
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Steve Guttag
We forgot the crackers Gromit!!!
![](http://www.film-tech.com/ubbmembers/268e.gif)
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-06-2018 09:01 AM
Note, I distinction between Enterprise drives and desktop/laptop drives is that an Enterprise drive should NOT re-read a bad area, it should mark the sector bad and move on since the other drives in the RAID have the data. When this happens, though, you'll get a hiccup in the image because the RAID thought it had the data from the drive that has an issue. In a desktop/laptop drive, that is not the scheme because it cannot presume there are any other drives to back it up...it will re-read to get the information, which in real-time can cause glitches on screen.
Generally, when there are glitches on screen...something is up with one or more drives. There are indicators for which drives are having issues (reallocated sectors that are either high are increasing daily, ATA errors, read times that are notably different than the other drives in the RAID since they have to work as a team). I've had them even then still have issues.
I've had drives that appear to be okay cause boot-up issues too. I'm a pretty staunch Hitachi (HGST) supporter. I've had some Western Digital (which now owns HGST) cause the odd boot up issues though their current "Gold" series seem to be fine. Seagate...well, they've let me down the most.
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