Zero Size or Corrupted Documents

[antonin]

Hi,

I have a Samsung Galaxy Tab 3 with Android 4.2.2 and CC 3.3.4

The library on my tablet is 1992 documents, and is a mix of pdf and epub documents. I have the latest version of Calibre on my PC, and have been successfully synching things for some time. All documents on the tablet are stored on a SD card.

Over the last few weeks, I regularly see several documents on the tablet report one of the following errors - "The document cannot be opened because it is corrupted or damaged" or "The document is empty (size 0KB)".

This is despite a transfer process (Connect as Wireless Device) that runs flawlessly and without error every time.

I'd be grateful for some help or suggestions. :-)

Thanks!

ant

[antonin]

BTW, the documents can be successfully read within Calibre, and I've even gone to the extent of deleting the documents from Calibre that resulted in errors in CC, importing them again in the database and then again uploading them to CC. The errors still occur.

[chaley]

If I read your second post correctly, then when you find a corrupt book on your device, then resending that book from calibre does not fix it even though the book can be opened in calibre. Is this right?

If so, then we are left with an uncomfortably large number of possible culprits.

• The book is not being sent properly from calibre. This can happen if calibre's temporary file system is full, or (shudder) if the calibre computer is failing.
• The book is not traversing the network correctly. Not sure why this would happen intermittently, and in any event calibre and CC would detect data being dropped or added during the transfer.
• CC is writing the wrong information. Again, not sure why this would happen intermittently, or why the behavior would change.
• The SD card is going bad. Data is corrupted either when written or read.
• The file system on the SD card is corrupt, so files written to the card are corrupted. This seems the most probable to me.

Resending the damaged book resulting in the same problem points first toward a damaged file system and second toward a failing SD card. The first possibility is especially true if the files are being reported as zero length. CC knows the length of the book it is receiving, so if the receive process finishes properly then CC received and wrote the correct amount of data. If it later is zero length then the SD card did that for you.

Regarding the second possibility: SD cards do wear out. A quality SD card should do "wear leveling", moving the data around on the SD card to avoid "bad spots", but even this will eventually fail. When they fail they give back bad data with no indication or warning.

Some inexpensive SD cards lie about their size, saying that they are larger than they really are, which causes no end of trouble. Is your SD card near full? Is it a quality brand name?

If I were you, I would:

1. Put the SD card into a card reader and check its file system using a "real" computer. It could be that the app AParted (Sd card Partition) can do this for you, but as I have never tried it I cannot recommend it. If your device supports mounting the SD card as a disk over USB then you can probably do the file system check that way.
2. While the SD card is in a reader and assuming the file system is OK, write a large file to the card then read it back. Do you get the same data back as you wrote?
3. If you have another card, try using it to see if the problem goes away.
4. Verify that the tmp folder on your machine running calibre is not running out of space.

Apologies for the stream of consciousness aspect of this reply, but unfortunately there isn't a definite answer to your problem.

[antonin]

Thanks! It definitely looks SD card related. I haven't had a chance to pop the card into a reader yet, but after deleting some other documents from it, I was able to transfer AND read some new documents. Thanks for your help!

[antonin]

So, I've purchased and installed a new SD card, and am in the processing of reorganizing my libraries. I've decided that the original card will contain reference books and docs, the newer one will be dedicated to magazines.

Question - is there a procedure or FAQ that deals with using multiple SD card with CC, and ensuring that it handles the change to the local library as cards are removed or inserted?

Thanks again!

[chaley]

Originally Posted by antonin

Question - is there a procedure or FAQ that deals with using multiple SD card with CC, and ensuring that it handles the change to the local library as cards are removed or inserted?

No, because CC does nothing special to support that use case. However, the default behavior might be good enough.

All of CC's processing uses its database. The only thing that requires the book to actually be present is reading the book. If you remove the SD card containing books, opening the books will fail. Same is true for magazines.

There are some potential problems. The first is that there is nothing that enforces your separation. Sending a magazine to CC while the "books" SD card is installed will work fine, and there is no mechanism to later move the book from one card to another. The second is that there is no built-in mechanism where CC shows you only books for which the files are available.

The first can be overcome by you being very careful. The second can be overcome to some degree if you provide a tag or custom column value to separate the books into their two libraries. An easy way to do this is to use calibre's virtual library feature and then allow CC to group on that information. See the FAQ answer How do I see/use my calibre virtual libraries in CC? for more information on how to do this.