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AJA hardware requirements

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Jackson Neelsam
AJA hardware requirements
on Nov 26, 2009 at 4:52:09 am

I am planning to buil a portable PC system to allow direct-to-disk recording with the AJA XENA 2K card. Currently there are tens of cameras outputting beutiful HD-SDI and there are many capable of doing it dual link for 444.

My concern is however to keep the system as small, efficient and silent as possible because it will require me to stay on set.

What is the minimum setup people are using here for a maximum of 10bit 4:4:4 recording from dual link HD-SDI?
I am planning to build an i7 920 2.66 based system, with lots of RAM and a decent graphics card. The list on the AJA site is full of Quadro cards which would be an overkill for a simple DDR.

I am not willing to get into dual xeons. First hand experiences regarding sufficient/insufficient system experiences will be highly appreciated.

thanks.

jack




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Tim Kolb
Re: AJA hardware requirements
on Nov 27, 2009 at 3:59:17 pm

The Quadro cards are on the list for compatibility reasons as well as power... I'd advise you to pass on installing a gamer card in a system you'll be depending on in a professional environment...

As far as configuration, you'll have the biggest bottleneck at the drives. Just because you can hang 4 GBit FibreChannel on a machine doesn't mean the drives will be able to ingest it all.

There are very big RAID 6 systems out there that will BURST to 400 MB/s, and claim 300 MB/s sustained. You'll need in the neighborhood of 260 MB sustained with audio and 3 color channels (you won't acquire an alpha channel). Keep in mind that many of those specifications for sustained throughput are done when the drive unit is below 50% capacity...many times WAY below. If the thing will just muster 300 MB/s on the first file being written, chances are good that your data rate will drop when it gets full. How much it may drop is a matter of testing each unit, but it's not out of the realm of possibility that you could drop below the minimum you need to keep ingesting on any but the most expensive systems.

So...I'd say:

1. Use what's on the approved component list if you expect tech support as those guys don't know about every component out there, they know about the components on their approved list...it's why they made the list in the first place.

2. Spend some serious time looking at the storage end of this scenario. That will be your biggest issue. Most computers are able to pass the bandwidth you'd need for this, but harddrives that can take it all in every day, all day long aren't as prevalent as the industry may have you believe...and the drive systems that can are typically dual power supply, multifan rigs that would not normally qualify as 'quiet'. AND storing 4 hours of footage at 10 bit 4:4:4 RGB uncompressed...so your RAID system will need significantly more net capacity than that to allow for data redundancy inside the drive unit, as well as keeping ultimate capacity as far above actual usage as possible to maintain speed.

3. How will you be redundant outside the main drive unit? If you show up as the data wrangler with an acquisition system, how will you protect the data? How large a battery backup (or backups) will you need to keep this beast running in the event of a power hiccup or failure? How will you backup the data? Each hour will be almost a terabyte...that's a lot of alternative storage. When will you back up? How much data will be at risk (only one copy) at any one time?

RAID 6 will be about the minimum drive configuration you'd want as a single drive failure on a 7 or 14 drive system configured as striped would wipe the entire system...but then you'll also need to carry hot swap replacement drives for your drive system for the occasion when (not if) one fails. Keep in mind that when one drive fails and the system needs to start restoring to a hot spare, that system's capabilities to do other things is limited until that process is done...and you want that process to complete before proceeding...

Lots to think about. But I'd move my emphasis from computer to drives...







TimK,
Director, Consultant
Kolb Productions,


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Alex Geroulaitis
Re: AJA hardware requirements
on Dec 5, 2009 at 8:54:52 am

Hard drives.

Assuming average single 7200rpm drive performance at about 100MB/s, falling off to 50% at the end of the drive, 10% overhead in RAID0 mode, 30%-50% in RAID5 or RAID6, you would need at least 10-12 drives to reliably achieve Tim Kolb's figure of 260MB/s of sustained writes across the array's capacity. There is no small chassis that would fit 10 drives (maybe 8).

You could use 4-6 drives in RAID0 and with a chance of dropped frames when the array is fragmented or full. If you are OK with that, then I would look at two boxes: an array like G-Tech eS Pro, and a decent single socket i7 system. They interconnect via 4-lane SAS (cheap, expandable, reliable).

I don't know if a graphics card matters much in a system used primarily as a DDR, and not for any graphics-intensive work.

Best,
Alex,
DV411


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Tim Kolb
Re: AJA hardware requirements
on Dec 6, 2009 at 2:19:33 am

[Alex Geroulaitis] "you would need at least 10-12 drives to reliably achieve Tim Kolb's figure of 260MB/s of sustained writes across the array's capacity."

...and I should probably say that I was calculating 4:4:4:4 RGBA uncompressed or 10 bit 4:4:4 RGB (comes out to about 248 MB actually)...8 bit YUV 4:2:2 will be much lower data rate, but dual-link and 4:4:4 was specifically mentioned...








TimK,
Director, Consultant
Kolb Productions,


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