Preparing SD cards for fastest write?

Question

Tell me if there's a more appropriate group for this. Anyway...

My friend flies RC airplanes, and has recently bought a "Keychain Spy DVR" at Ebay for something like $16. The good news, aside from the $16, is that it shoots 720x480P video, with audio, at 30 fps for about 50 minutes on one battery charge, with a 4GB micro SDHC card. So he just attaches this sucker on the wing or fuselage, and comes up with some very nice video. Youtube has lots of examples of these videos - search on 808 camera, or 808 keychain.

There's a fairly long list of bad news items, one of which is that the video stutters, pauses, or jumps now and then. So it will be going along smoothly, but then seems to freeze, then jump ahead, with something clearly being lost. But this is in the video only, not in the audio, which is glitch free. Analysis by others in VirtualDub indicates the frozen stretches are indeed duplicate frames.

On the chance it might help, my friend bought a class 6 SDHC to use with this camera, and indeed it did seem to significantly reduce the stuttering at first. But with more use, the improvement doesn't seem so great.

In researching this, I've come across SD Formatter, available here:

formatting link

One of the formatting options is to fully "erase" the card. Now I know that NAND-gate flash memory can read randomly, but has to be erased, in blocks, before a write. So once you fill up a new card, deleting the files, or even formatting the card, may still leave you with a card that's pretty much completely un-erased, and I would think that would slow down any subsequent write process, which for this camera is proceeding at 1.3MB/sec.

Can someone confirm that the SD card keeps track of which blocks are currently erased. In other words, it doesn't automatically erase every block it writes to. If it keeps track, then erasing everything ahead of time might speed things up.

Does using the full erase formatting option reduce the life of the card materially?

I'm doubtful that slow writing is the primary cause of the freezing video, but it's possible that for $16 you don't get a lot of multi-tasking, and if writing to memory could be speeded up, maybe whatever IS causing the problem would happen less often.

And for those interested, the definitive source on this camera is here:

formatting link

Thanks for any ideas.

Vladimir Vassilevsky · Accepted Answer

The card controller can do a variety of different things, and you don't have much control about it. The general recomendations are:

1) Try different card makes and different vendors. 2) Use basic file system FAT16/FAT32 with clusters of maximum size. 3) Start with empty card to avoid fragmentation issues.

The 1.3 MB/s is not much; this speed should be easily sustainable unless something is wrong with hardware or software.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

formatting link

Adrian C · Answer

Can't offer much ideas on the preformatting of your cards, but if you look at reviews of class 6 cards there does seem to be some variation of actual speeds attainable.

I'm investigating getting a Class 6 card for my MD80 clone (the 720x480 gumstick model). I've also got one of the car remote fob types in the post coming here. So will be messing about with installing it in the car, adapting power and changing the card size to SD.

Thanks for the link. Very interesting; these things made of market failed mobile phone parts :-)

Preparing SD cards for fastest write?

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