Let's talk about the XQD memory card format

[Darren Levine]

It's been for the most part irrelevant, but now the FS7 is using it as it's primary recording media. While speed and reliability are indeed crucial for such a camera, the lowly SD card has proven itself very useful, and with the 280mb/sec sandisk SD cards, was SD really not feasible for the FS7?

The FS7 does have an SD card slot, but it's reportedly not for recording purposes.

at this time, prices for slower XQD are around 2-300 bucks for 64gb, haven't seen word on pricing for the new, faster version. the 280mb/s 64gb sandisk SD is $230

So, will the cost per gb remain high because next to no one is using this format? seems so for the time being.

I'd gather that the xqd-h will be 350+

 

[FrameFarmMedia]

After having CF cards crap out on me I am kinda looking forward to a pro media format and XQD is cheaper than SxS.

It looks like the XQD S cards will work for al 4K shooting modes. The cheaper N cards are good for HD recording. I could see grabbing a bigger cheaper N card for the HD jobs which tend to be longer records.

 

[Eric Coughlin]

GH4 4K at 100mbps (12.5MB/s) from what I've heard works fine on 45 MB/s SD cards. I don't understand why the N Series with "Write Speeds Up to 80MB/s" can't even record the 100mbps (12.5MB/s) 4:2:0 4K on the FS7, along with the 220mbps (27.5MB/s) 10 bit 4:2:2 4k.

When the GH4 came out new higher speed memory cards were released at the same time which people eventually found were not needed as lower MB/s cards could be used. Could this be the case and the N-series cards will be capable of handling anything the FS7 can record internally?

 

[Phil vG]

Sandisk have come out with a 90MB/s 512GB SD card. Not cheap, but there might be some price drops in competition to that.

 

[starcentral]

Guys I shoot 4K (4096x2160 not 3840x2160) @ 60p (600Mbps) on my F55 to XQD 180MB/s cards no problem. HFR is 3 times the frame rate, but 4 times less resolution, so it's a wash.

The new cards, the 400MB/s (3.2Gbps) ones are faster but won't make any difference for recording (unless Sony is planning 4K HFR... ) but they will make a difference for offloading speeds which is especially good considering the newer cards are 128GB in size.

 

[AtticusLake]

Just a note first: the convention is that lowercase "b" means bits, and capital "B" means bytes. (And "m" is milli, where "M" is mega.) So 90 Mb/s would be 90 megabits per second, or 11.25 megabytes/sec. Anyhow...


SD would have been iffy as the medium for the FS7, since you can be doing up 600 Mb/s, which is 75 MB/s. While the fastest SD cards can theoretically handle this, the issue is consistency. The filesystem in an SD card (or any other kind of drive) is organised as blocks (typically a few kB in size) linked together to make files, with data stored in other blocks to say how they are used within a file, and other blocks in different places storing info about the file itself. So writing can involve non-sequential updates to the drive, even in the absolute best case when you open a file and write straight data to it (like video recording).


The problem is that SD cards can only write an "erase page" -- typically 2MB or 4MB, much more than one block -- to the flash at once. So you get this long period where you're basically writing to a RAM buffer in the card, then this hiccup when you hit a different erase page, and the RAM buffer has to be written to flash. That's why people like lots of safety margin in the speed of their cards -- e.g. Eric mentions 100 Mb/s recording on 45 MB/s (360 Mb/s) cards, which is a 3.6x safety factor. If you push the card closer to its speed limit, this is one of those things that might work most of the time, but occasionally catch you out.


I have no idea what a "good" safety factor would be for SD, and it almost certainly depends on the internal design of the card -- not just the published speed numbers. You definitely want to watch out when they talk about speeds "up to" some number. We don't care what the speeds are "up to"; we only care what they are "down to". In other words, what is the MINIMUM speed the card GUARANTEES, not what is the best peak speed it might reach at some point during your recording.


Bottom line, SD is a technology that has been stretched far beyond its original purpose. XQD cards are designed for purpose, and supposedly better than this in terms of how the controller within the card manages writes, and so should give more consistent performance.


In particular, according to these slides:


http://provideocoalition.com/awilt/story/122-slides-on-the-sony-pxc-fs7/P2


the S-series cards (and not the N-series; look for the "E" at the end of the part number, as in "QDS64E") have extra cleverness inside them (the "EB Stream function") to guarantee continuous writes at a sustained rate. This will involve cleverer hardware, and probably more RAM, in the card; so it certainly isn't free.


So it looks to me like XQD is worth it, and the S series in particular is really designed to remove the basic problems with flash memory to work for video. Personally I would be much happier with a storage technology that was specifically designed for this application.


As for the new G series cards announced at the same time -- I have no idea if we are supposed to be using those for the FS7, but the slides seem to be saying that S series are good for all FS7 speeds. [edit] Actually it looks like you might need G series for 180 FPS, which isn't covered in those slides.

http://blog.sony.com/press/sony-unv...-4k-xdcam-camera-with-a-super-35-cmos-sensor/

 

[combatentropy]

SD is a technology that has been stretched far beyond its original purpose.

For that matter, all technology has been stretched beyond its original purpose. I see no reason why the guts of the SD card cannot keep getting improved, as they so far have been.

I would say that you can rely on the speed class rating of a name brand card. The older speed class rating (2, 4, 6, 10) means the minimum, sustained write speed. The newer speed class ratings (UHS 1 and UHS 3) mean write speeds of at least 10 or 30 MB/sec. (https://en.wikipedia.org/wiki/Secure_Digital#Speed_class_rating)

It is in our interest to have as few different kinds of media as possible. If our cameras use the same card as everyone's phone, then our cards will be cheaper. If our cameras use the same card as our laptop has a slot for, then our workflow will be simpler (oh no, I'm in the Sahara and forgot my XQD card reader).

Use whatever card you have to right now. If it's XQD, use XQD, I guess. But as far was what we want, I think we want the SDXC card to continue improving. Failing that, if it can't quite keep up, I think we want our cameras to have their own buffer, like the Digital Bolex does, for example. I would rather wait for five minutes after shooting 120 fps, to let the camera finish writing it all out to the card, than to deal with expensive, specialized cards.

IMHO. YMMV. I've been known to be wrong. Etc., etc.

 

[AtticusLake]

... I see no reason why the guts of the SD card cannot keep getting improved, as they so far have been.

Very true; but they're still cheap, and designed for the corresponding market segment. And you can't improve the internals beyond the limitations of the interface.


The UHS-II bus on SD cards goes up to 312 MB/s transfer speed maximum, which is not as fast as the new G series XQD cards. XQD can theoretically handle 1000 MB/s, which gives it a lot of room for growth. That's down to XQD using a different bus (PCI Express), which makes it physically incompatible.

I would say that you can rely on the speed class rating of a name brand card. The older speed class rating (2, 4, 6, 10) means the minimum, sustained write speed.

Knowing a little about how these cards work internally, and having done a lot of testing of various SD cards, I would have to say I would have reservations about that. I think there's still scope for glitches.


I was benchmarking eMMC chips (basically an SD card on a chip, so you can put it on a circuit board; the storage in your phone or tablet is probably eMMC) for a consumer product. We compared two chips, with the same "sustained speed", and they did indeed deliver the advertised speed. But when installed in the product, one of them was *way* slower than the other, to the point we couldn't use it. This was a blow, because (surprise, surprise) it was the cheap one. The difference was the internal buffering, which meant that when the use case was a little different, it suddenly needed to flush its buffer all the time, which killed speed.


The point is that you can always justify good numbers to put on the brochure; but those numbers don't always match the real-world performance. Particularly when you want true reliability -- when shooting video, you don't *ever* want the card to glitch and drop a frame or two.

It is in our interest to have as few different kinds of media as possible. If our cameras use the same card as everyone's phone, then our cards will be cheaper. If our cameras use the same card as our laptop has a slot for, then our workflow will be simpler (oh no, I'm in the Sahara and forgot my XQD card reader).

Absolutely, couldn't agree more. I HATE having to have multiple formats of stuff; like I only buy portable electronics that run on AAs, for example, if at all possible. I don't know why the world needs both CFast and XQD -- and both published by the same body!


But the new cameras need fast, reliable storage. Sony really seem to have done some work on this, and my feeling is that XQD is a genuine step forwards from SD, at least.

 

[starcentral]

That press release indeed makes it seem like you need the G series cards but you shouldn't need it data rate wise to record 180 fps.

I'm doing it on the F55 with the 180MB/s S series XQD cards without any issues. Remember 180fps @ 2K is less data rate than 4K @ 60p...

Sony XAVC White Paper

Anyway, time will tell,....

 

[harddrive]

That press release indeed makes it seem like you need the G series cards but you shouldn't need it data rate wise to record 180 fps.
,....

From the FS7 thread - http://www.dvxuser.com/V6/showthrea...corder&p=1986476144&viewfull=1#post1986476144 :

Just got the scoop from Juan Martinez on the difference between S and G cards. The camera can shoot S cards in all resolutions. The advantage of the G card is double the transfer speed for copy or ingest.

I currently use SDHC cards to record XDCAM 35Mbs and it's been without a problem - and the big advantage is the cards cost about the same as a DVCAM tape and I can treat them in the same way - as a consumable item, not capital.

BUT... that's for 35Mbs. Here we're talking about vastly higher data rates. There's also the physical aspect to consider, SD cards do just seem a little small and flimsy for pro use, though pro stills guys use them all the time. I'm prepared to accept it for the huge workflow advantages to me over SxS, but if I needed very high speed, large cards (when even SD gets expensive) I'd want to pay a little bit more for robustness/reliability. And XQD seems a pretty good compromise then.

 

[Mitch Gross]

Knowing a little about how these cards work internally, and having done a lot of testing of various SD cards, I would have to say I would have reservations about that. I think there's still scope for glitches.


I was benchmarking eMMC chips (basically an SD card on a chip, so you can put it on a circuit board; the storage in your phone or tablet is probably eMMC) for a consumer product. We compared two chips, with the same "sustained speed", and they did indeed deliver the advertised speed. But when installed in the product, one of them was *way* slower than the other, to the point we couldn't use it. This was a blow, because (surprise, surprise) it was the cheap one. The difference was the internal buffering, which meant that when the use case was a little different, it suddenly needed to flush its buffer all the time, which killed speed.


The point is that you can always justify good numbers to put on the brochure; but those numbers don't always match the real-world performance. Particularly when you want true reliability -- when shooting video, you don't *ever* want the card to glitch and drop a frame or two.

You have just very accurately described one of the main resins we required the use of our SSDs on the Odysset7Q.

 

[Eric Coughlin]

I would say from a certain point of view cheaper less reliable cards can actually be more reliable. The camera has a dual record feature which I would use, that is, if I can afford enough memory to use that feature. With the C100 and SD cards I regularly use dual record mode. If I can't afford enough memory, then I won't use the feature.

Let's theorize that an SD card has a 1/100 failure rate per shoot and an XQD card has a 1/1,000 failure rate per shoot. If I'm recording dual record with SD cards then the chances of both cards failing is 1/10,000, and then let's say that the XQD cards are too expensive to use the dual record mode, so the chances of failure are actually higher at 1/1,000.

 

[harddrive]

I would say from a certain point of view cheaper less reliable cards can actually be more reliable. The camera has a dual record feature which I would use, that is, if I can afford enough memory to use that feature. With the C100 and SD cards I regularly use dual record mode. If I can't afford enough memory, then I won't use the feature.

Interesting point, and it reminds me of why I normally use SD cards instead of SxS. The SD cards themselves may be less reliable - but I'm increasingly convinced the single most possible point of failure is not any form of hardware, but finger trouble. Incorrect deletion and formatting of a card before the content has been made use of, and a producer I worked with last week had recently had exactly that happen to him with some P2 material. Use an SD card, treat it like tape, and there's no rush to reuse the card.

This is a little different - the XQD cards are dear enough that you can't work in that way - but I see your point. The danger remains of inadvertently formatting both cards by mistake though.....

The only thing I wonder is if in the case of a single card stopping recording, will the camera stop recording to the other card as well?

 

[Mitch Gross]

I would say from a certain point of view cheaper less reliable cards can actually be more reliable. The camera has a dual record feature which I would use, that is, if I can afford enough memory to use that feature. With the C100 and SD cards I regularly use dual record mode. If I can't afford enough memory, then I won't use the feature.

Let's theorize that an SD card has a 1/100 failure rate per shoot and an XQD card has a 1/1,000 failure rate per shoot. If I'm recording dual record with SD cards then the chances of both cards failing is 1/10,000, and then let's say that the XQD cards are too expensive to use the dual record mode, so the chances of failure are actually higher at 1/1,000.

That is a statement of functionality, not technicality. It is pretzel logic.

 

[Mitch Gross]

Part of what is ignored in the above comparisons is the quality of recording from the different formats. Yes there is a more highly compressed form of XAVC available to squeeze onto the slower XQD cards, but what do you give up? How does the quality compare to the less compressed versions and how does it compare to 4K ProRes? If all I cared about was fitting as much material as possible into the smallest container, I would shoot the crappiest format possible and not worry about it taking up any space. Of course we all can't shoot uncompressed RAW either as it is not practical, but we cannot simply equate the technical quality of every available compressed video format. There absolutely are differences and we should respect that and determine what works best for our needs.

 

[joe1946]

The new Panasonic HC-X1000 4K Camcorder shoots 4K UHD @60fps and still only uses low cost UHS-1 U3 cards like the GH4 so with the much faster 1866x UHS-II SDXC cards from Sandisk and Panasonic there is no reason why SDXC cards could not be used on most Pro 4K camcorders.
http://www.bhphotovideo.com/explora...000-4k-camcorder-packed-professional-features





Even micro SDXC cards come in UHS-II fast speed for future compact 4K cameras.


Panasonic now has UHS-II SDXC P2 cards.



http://www.bhphotovideo.com/c/product/963983-REG/panasonic_aj_p2m064ag_64gb_microp2_fast_memory.html