MobileRead Forums - View Single Post - 903 microSD write fails on PocketBook 903

LoneTech · 01-03-2011, 01:39 AM

dd is an ancient copy command, the meaning of the name has been lost to history (although the guess "data duplicator" is around). Its original use was to transfer data to and from tapes that were particularly picky about how large chunks you could access, and it can also do translations for IBM mainframe data, padding, byte swapping and such. In this case, however, it is simply copying a disk, sector by sector, although I chose somewhat larger transfer sizes. The PocketBook basically overrode the block size anyhow, since it buffers several megabytes and writes at whatever pace it picks. One feature of dd is the final report of how fast it worked.

Accessing the internal memory on the PocketBook (called Device in the GUI, Pocket903 as exported or /mnt/ext1 in the OS) works fine, I've written files there with no problems. This indicates that the USB storage system works normally, and the problem is specific to the SD slot driver - though probably dependent on card type.

That thread does look like the same behaviour. It's a late symptom, however, as all it's saying is the USB storage device disappeared. It happens for me too, at some point after the PocketBook internally realizes something is wrong, but there's no telling what.. and things have gone wrong earlier, as evidenced by my misplaced data.

I just tried the Configuration - Maintenance - Format SD card choice in the PocketBook. It did not erase the card, I'm not sure it overwrote anything at all. It did, however, jump into digitizer calibration. I do not know if that's expected.

I have a couple of other microSD cards to test with, though one appears broken and both are tiny. The whole point of installing the card was that my books wouldn't fit otherwise.

The card image thing was mostly to eliminate other factors. I am estimating that the problem is more likely to reoccur, not less, with any other access pattern except very slow access limited to one sector at a time.

I have now tested one of my SanDisk 128MB TransFlash cards. It appears to have no problem at all. The format command did wipe this one, and triggered a calibration as well. The problem may be SDHC specific, and seems most likely to occur on large and slow cards.

I must point out that I do not believe my use of Linux affects this at all; how to write to the SD card is out of the computer's hands once the data has moved over to the PocketBook.

I probably could purchase a card with less trouble, but that would not fix the root cause. The card itself is not defective, as it works just fine in every other card reader I have. The only way it would be prevented is having a card that consistently outperforms the PocketBook's attempts to write, so it never gets its buffers full; and that's a very hard guarantee to make. We don't know how fast it attempts, and cards aren't typically rated so you can be sure. In particular, SD class only covers whole erase block recording such as done by video cameras. On the other hand, it's possible the bug is specific to SDHC cards that do not have the write rate information. I just don't know.

01-03-2011, 01:39 AM	#12
LoneTech Zealot Posts: 135 Karma: 7767 Join Date: Oct 2010 Device: PocketBook Pro 903	dd is an ancient copy command, the meaning of the name has been lost to history (although the guess "data duplicator" is around). Its original use was to transfer data to and from tapes that were particularly picky about how large chunks you could access, and it can also do translations for IBM mainframe data, padding, byte swapping and such. In this case, however, it is simply copying a disk, sector by sector, although I chose somewhat larger transfer sizes. The PocketBook basically overrode the block size anyhow, since it buffers several megabytes and writes at whatever pace it picks. One feature of dd is the final report of how fast it worked. Accessing the internal memory on the PocketBook (called Device in the GUI, Pocket903 as exported or /mnt/ext1 in the OS) works fine, I've written files there with no problems. This indicates that the USB storage system works normally, and the problem is specific to the SD slot driver - though probably dependent on card type. That thread does look like the same behaviour. It's a late symptom, however, as all it's saying is the USB storage device disappeared. It happens for me too, at some point after the PocketBook internally realizes something is wrong, but there's no telling what.. and things have gone wrong earlier, as evidenced by my misplaced data. I just tried the Configuration - Maintenance - Format SD card choice in the PocketBook. It did not erase the card, I'm not sure it overwrote anything at all. It did, however, jump into digitizer calibration. I do not know if that's expected. I have a couple of other microSD cards to test with, though one appears broken and both are tiny. The whole point of installing the card was that my books wouldn't fit otherwise. The card image thing was mostly to eliminate other factors. I am estimating that the problem is more likely to reoccur, not less, with any other access pattern except very slow access limited to one sector at a time. I have now tested one of my SanDisk 128MB TransFlash cards. It appears to have no problem at all. The format command did wipe this one, and triggered a calibration as well. The problem may be SDHC specific, and seems most likely to occur on large and slow cards. I must point out that I do not believe my use of Linux affects this at all; how to write to the SD card is out of the computer's hands once the data has moved over to the PocketBook. I probably could purchase a card with less trouble, but that would not fix the root cause. The card itself is not defective, as it works just fine in every other card reader I have. The only way it would be prevented is having a card that consistently outperforms the PocketBook's attempts to write, so it never gets its buffers full; and that's a very hard guarantee to make. We don't know how fast it attempts, and cards aren't typically rated so you can be sure. In particular, SD class only covers whole erase block recording such as done by video cameras. On the other hand, it's possible the bug is specific to SDHC cards that do not have the write rate information. I just don't know.