dropped frames, slow raid write rates

[Bob Zelin]

why do you make a post like this without saying EXACTLY what SATA RAID and SATA host disk drive controller card you have in your computer (oh, I know why – because you believe that these are all commodity items, and no matter what the advertising budgets – they are all the same).

If you were working in DVCProHD or ProRes422HQ, even with those slow rates, you would still have no problems. But I bet you are digitizing at uncompressed HD. And that is why you are getting dropped frame errors. I hope to God that you are not using the Apple XServe RAID. It’s Sunday, so this is my suggestion if you are using an Apple XServe RAID for this system. Take your XServe RAID and walk it (drag it) over to your trash can. Tomorrow, order 3 internal SATA drives (at $140 a piece) stripe them together and go back to work. Otherwise, buy a modern SATA array (or fibre array) and go back to work.

(But I spent $14,000 when I bought this damn array) – well TOUGH NOOGIES – it’s a piece of crap. It’s over. Spend $500 for 3 raw SATA 1 TB drives, and have a better product.

bob Zelin
ps – your dual 2.7 will be useless in September 2009, so get ready to buy another computer.

[Bob Zelin]

Hi Jason –
well, I reread your post, and I am an idiot. You said that you have an 8 drive SATA array – and you erased everything and now have 2 Terabytes. So you do not have an XServe RAID – you have an older 8 bay SATA array (I can’t guess what one you own), but you must have eight 250 Gig SATA drives, all stripped together. You are getting 160Mb/sec write speed – which is barely enough to do uncompressed HD. Even though you need a theoretical speed of 118Mb/sec to do this, you need over 200Mb/sec for sustained playback. You said that it “used” to work – but at 160Mb/sec – you are pushing it. Again, 3 modern SATA drives in a new MAC Pro stripped RAID 0 will give you a higher data rate than this. I know its easy for me to say “spend money”, when it’s not my money, but the data rate you are getting on an old PCI-X system with older 250 Gig drives sounds typical, not slow for what you own.

BobZelin

[Walter Biscardi]

[Jason Longo] “When I ran the AJA system test without the “Simultaneous KONA DMA” box checked, I get write rates of 160mb/sec and read rates of 215 mb/sec. When I check the “Simultaneous KONA DMA” box those rates drop to Write 44mb/s and read 98mb/s. “

Those speeds are barely enough to capture Uncompressed HD. You need a bigger, faster array if you want to work there or a different type of connectivity to the Mac to increase the speeds. Drop down to ProRes and you should be fine.

Years ago I had an 8 drive, 2TB Medéa Ultra SCSI array that ran something like 270MB/s so it worked fine for Uncompressed HD, but that was a very fast, 2 channel connection to the Mac.

Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.

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[Ramona Howard]

Jason,

8 drives should yield more than 160mbs, I would check to see if you have a slow or failing or even failed drive in the mix.

I can’t totally speak for how this all works in the MAC world but I can say from MANY years of experience that slow arrays stem from several reasons no matter what they are connected to. If you were once able to capture uncompressed with that array (which I do believe you were) then something has gone amuck.

Simply suggesting to drop to a COMPRESSED format like ProRes isn’t a good suggestion (Maybe this guy really needs uncompressed). It is a fairly decent codec but it isn’t uncompressed quality by an means.

Here are some suggestions and if all else fails you could always call in help from people like Bob Zelin, who make a living doing this on the MAC.

Again, I can only make suggestions based on what I am familiar with here

Does the hard drive controller in your system allow for configuration? If so a wrong setting will certainly effect drive speeds.

A controller in an improper slot in the Mobo, or one that is contention with another device will certainly cause problems (drop frames being a big one)

Again, physical drive issues in the array. Drives are not designed to just sit for lengthy periods of time once they have been in use. Drives have gotten better over the years but I am guessing your array is several years old 🙂

Capturing the wrong flavor of uncompressed with an array that isn’t fast enough. For example there is a huge difference in needed thruput for 8bit YcbCr (YUV) than for 10bit RGB.

Try wiping your array clean and re-formating.

Hope that helps a bit, good luck

Ramona

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