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OT: PCI-X 64 bit question
This isn’t directly SAN or NAS related (but sort of is). On another forum (not Creative Cow), some folks are claiming that a certain HD hardware I/O card that does real-time video and DVE processing and requires a 566Mhz, 64-bit PCI-X slot, has a bandwidth “bottelneck” of 175MB/sec.
But…this particular card can do 2 streams of real-time, uncompressed HD using an optional dual-channel SCSI daughtercard (requiring upwards of 250MB/sec), and can do multiple compressed HD streams using either the SCSI option or SATA based storage.
These folks are saying on the one hand that the card can only handle 175MB/sec, but then they’re saying it can do uncompressed HD requiring over 200MB/sec.
They go on to argue that you can’t use shared storage with this system because of this PCI bus limitation, but you can use direct attached SATA and get multiple compressed streams of HD and up to 8 streams of uncompressed SD.
None of this makes sense to me. I’m no electrical engineer but I know a little about how a computer works.
My question:
If the card meets the PCI-X 2.0 spec, why would it not be able to use the speeds the spec is capable of, which are roughly 537MB/sec sustained according to all the specs out there.
Also, how could it do 2 streams of uncompressed HD requiring well over 200MB/sec, and 8 streams of uncompressed SD at well over 160MB/sec (plus some processing overhead) if the card’s speed bottleneck is stuck at 175MB/sec?
Thanks for any feedback. I’d like to answer in the other forum with some ammunition (or with my tail between my legs)
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com -
6 Replies
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you can’t get this bandwidth. I wish you would point to the forum that is discussing this. I have clients that use toy HD cameras, and tell everyone that they are doing full HD production, as if they have Sony F23 cameras and SRW decks. “Of course we do uncompressed HD – thats why we use AVID” – not understanding what DNxHD145 even means.
You know I love to start trouble – I wish you would point me at this forum.
Bob Zelin
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Bob..I wouldn’t do that to them! Just kidding.
The card in question is the VelocityHD. It can indeed do all the things I listed, 2 streams of uncompressed HD (using their optional SCSI daughtercard only), multiple streams of compressed HD, and up to 8 streams of compressed SD and 4 streams of uncompressed SD.
The argument on the other forum is that people are saying the card has this theoretical 175MB PCI bandwidth limitation. They say it’s because the card is a 64bit, 66Mhz card…which also doesn’t make sense since that PCI spec supports speeds to 533MB/sec and can in practice deliver well over 250MB/sec throughput.Anyway…the argument came up because people on the forum claim you can’t use a SAN or 10GB ethernet NAS with the VelocityHD..and I responded with, “why not?”
These same people told me we could not use shared storage of any type with our older VelocityQ systems, much less a Gig-E NAS based one like we’re doing. So…we proved them wrong on that one. I just don’t understand why a SAN or 10GB ethernet solution that’s properly configured would not work with these newer VelocityHD systems if a dual-channel SCSI card they provide will give 2 channels of uncompressed HD.
Now few people edit uncompressed with this system…so that’s kind of a moot point. The bigger issue is they still say you cannot use shared storage to edit compressed HD. I just don’t understand why.
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com -
“they” say that because these are salesmen that tell them this, and they WANT THEIR COMMISSION. Before Final Share/Apace/MetaSAN/EditShare/Facilis, these very same people said “you have to have AVID Unity”, or “you have to have Apple XSAN”. Why – BECAUSE THEY WANT THEIR MONEY.
I don’t have the link anymore, but I had a recent link from the Apple Knowledge Base that said that Fibre Channel was required for shared storage solutions.
Command Soft (TransSoft) should be thanked profusely for first proving that you don’t need to spend a fortune for shared storage – they were the first alternate to AVID Unity storage. Personally, I thank Lance Bacheldor (creative Cow contributor) for first telling everyone (and me) about “do it yourself” ethernet shared storage for FCP. I can credit Tiger Technologies, and I can credit Small Tree, but if it was not for CREATIVE COW, I would never know about the possibility of such a solution, and Lance’s early experiments in doing this.
At the end of the day, I say THANK YOU CREATIVE COW.
Bob Zelin
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Yup..same here. I was so confused about shared storage back when we were researching it that I had begun to think that the $20,000 we had budgeted for it was woefully low. Until I started asking questions on this forum.
And it’s funny, but I told people in the other user group the same thing about marketing and sales. I said the company tells them they have to have the SCSI daughter card because they want to sell another product to them!
It’s like when my wife tells me an insurance salesman or doctor or car salesman was really nice to them. I tell her..”yeah..because they want to sell you something!” Let’s see how nice they are when you decide not to buy!
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com -
It’s a video i/o card with the drive array direct attached to the card/daughter card.
the link from the array to the card therefore isn’t the bottleneck it card>computer.
Thats what I take from it anyways.
s
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Yes you’re right in how you understand their “theory.”
My cohorts are arguing that because of that “bottleneck” on the card’s PCI bus (the card is a 64 bit, 66Mhz card) you cannot use shared storage and get the same performance as you can with the SCSI card/drive array configuration.
My argument is if the shared storage is coming from a SAN via fiber channel HBA or 10GB ethernet, as long as the data throughput is as fast as what the SCSI is delivering, and there’s no latency, in theory a SAN or 10GB NAS could deliver the same performance.
We’ve already proven this works on the SD version of this hardware/software (VelocityQ) because we have 3 of them in our facility editing happily with an Apace vStor via GB ethernet. We were consistently told it wouldn’t work. 2 years in, I can say it works GREAT. We get 8-12 channels of DVCPro50 compressed SD video across 3 edit systems and can get about 4 channels of ucompressed (which we virtually never use).
The VelocityHD uses a card built on the exact same architecture as the VelocityQ, but uses a new compression scheme and different software drivers for the card. Harris has literature that says you HAVE to use their SCSI card to get 2 uncompressed HD streams. But the card was developed in 2002-2004, long before people were achieving the speeds we’re now commonly seeing in affordable SAN and NAS systems.
My point to the other forum was that if you could feed data fast enough (500MB/sec and up), there’s no reason why a SAN or 10GB NAS couldn’t do 2 uncompressed HD streams same as the direct attached SCSI. The computer is agnostic about how that data is getting to it, and as long as that data doesn’t compete on the same bus as the VelocityHD card, it should work.
I don’t know for sure that it would work, but whether the data’s coming from dedicated SCSI or fibre channel or 10GB ethernet, as long as the sustained speed is there without latency, it should.
That’s sort of what I was wanting someone to confirm or tell me I’m wrong about. I trust the folks in here in regard to this stuff.
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
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