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Author Topic: 32GB SDCard, choppy records  (Read 2848 times)
ptosch
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« on: September 11, 2009, 09:17:24 AM »

Hi !

I am experiencing strange problems with my 32GB SDCard.
When recording from my dreambox500 to the sheevaplug using cifs to a usb-attached harddrive there are no problems.

But when I try to record to the 32gb card, the recording is very choppy, after half an hour the dreambox even stops the
recording with the message "write error on share".

- I tried using cifs- and nfs-shares, no change, still choppy:
- I put the card into a card reader and attached it via USB to the sheevaplug, still choppy;
- The card has been tested; it was filled completely with a file, then compared with the original: no problems;
- When i copy manually files to the sdcard while attached to the plug there are no problems as well;

Some more info:
- the streaming is never more then 800kb/sec, the card is capable transferring 4MB/sec;
- i used sheevaplug-installer-alpha-6 on the plug
- i even used a kernel with sdcard slowdown, no change

some observation on the plug:
- while recording on the USB-Harddrive one can see regular flickering of the Network-LED,
- when using the sdcard one can see irregular flickering. There are breaks in the transfer up to 8 seconds. Watching the  increase of bytes of the recording files looks very similar: after regular growing of the file, there are often stops of ten seconds in the increase;


first guess:  The card is too big, the plug has too much DMA overhead, or something
second guess: SD Cards write with a certain block-size, which has to be set ... or something

Unfortunately i find my guesses not really logical, since copying a simple file over network to the file works smoothly.

What do You think about it ? Every guess is welcome.

cheers,

 Peter
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DamonHD
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« Reply #1 on: September 11, 2009, 10:06:49 AM »

Sounds like write 'stuttering' as can happen on solid-state media that has been filled at least once.

If you could make your transfer/write block size (at least) the card's internal block size (remembering that many units may be in parallel inside) then possibly your stuttering would go.

Rgds

Damon
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ptosch
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« Reply #2 on: September 14, 2009, 01:06:39 AM »

Some news,
Actually I tried the combination of ReiserFS and CIFS. Now it is much better, though it stutters every 2-4 minutes for a half second.
I still have to change the block size, however I donīt know how to find the internal block size of the sdcard.
Cheers,

 Peter
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DamonHD
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« Reply #3 on: September 14, 2009, 03:01:34 AM »

My *guess* is that if you can write in blocks of 256kB+ then much of the problem will go away.

Rgds

Damon
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Rabeeh Khoury
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« Reply #4 on: September 15, 2009, 11:00:39 PM »

which kernel are you using on the plug? The original or 2.6.30.x?
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ptosch
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« Reply #5 on: September 16, 2009, 01:48:16 AM »

uname -a:

Linux hostname 2.6.30-rc6 #2 PREEMPT Wed May 20 05:42:04 MDT 2009 armv5tel GNU/Linux

I have to find out how to raise the block size for reiserfs, so results follow later.

By the way:  does anyone know how to set reiserfs flash-memory friendly ?

regards,

 Peter
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DamonHD
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« Reply #6 on: September 16, 2009, 02:11:15 AM »

Would a large commit=XXX help?  I have mine set to 600 for ext3 to attempt to better batch up writes.

Rgds

Damon
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