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I recently bought a 16 GB "Sandisk Ultra" Compact Flash card for my camera. I always do some testing on new storage devices before starting normal use: first some scanning, then maybe a copy of the first few megabytes to preserve the original factory state, then badblocks.

The initial scan was done with hexdump command "hd /dev/sdc" which IMO should output a few dozen lines of text for the partition table etc, then report all "0x00" until the end of the drive.

Now what I found out is the first 64 megabytes was normal like above, then after the 64 MB boundary the card was filled with some data. It appeared to be a random pattern; I ran a recovery software but did not find any files. The last 512 bytes of the card were empty again (0x00).

I did a complete copy of the whole card with dd for reference or whatever (probably will get rid of it). If I remember I did a second readout of the whole card and it was consistent, md5 sums matching. Then I tested the card with badblocks with no errors, started using it, took about 3 gigabytes of pictures and everything still OK. The speed appears to be also fine, the card was advertised as 50MB/s read and 25MB/s write. I have no USB3 but on USB 2.0 the write speed was around those 25 MB/s and the read speed close to 30 MB/s (probably the max possible on my hardware).

So, in short, my question is if it can be normal for a brand new CF card to have some random pattern instead of 0x00.

Any new media I have tested this way until now was "empty": usually 0x00, once I saw a pattern of 0x00 with a few rare repetitive sequences of something else, I think maybe I also saw 0xff instead of 0x00 (not sure). Once I found normal data after the first 100MB on a hard drive (which I returned), once a random pattern on the last few sectors of a USB pendrive (that pattern was not matching in consecutive reads and the drive eventually failed).

  • This does not seem related to Unix/Linux. Probably needs to be moved – Randomhero May 8 at 10:21
  • Depends where you did buy your card. I remember having wedding pictures on a brand new card I bought in Cambodia :D – darxmurf May 8 at 11:23
  • Could that be remainings of an in-factory testing process ? – Httqm May 9 at 9:13
  • I do realize the question is OS-independent. If You can suggest a better place to move it, I would appreciate. – Old Aperture May 11 at 16:45
  • I bought the card in Poland, from an online store. The packaging seemed very much all right, the transfer speeds are OK. The card looks genuine to me. – Old Aperture May 11 at 16:49

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