| 1 |
On 6 Feb 2009, at 05:28, Iain Buchanan wrote: |
| 2 |
> It's a Lexar Media 512Mb SD card, a couple of years old. Yes I know I |
| 3 |
> can get a cheap 2Gb for <$20 but I'm more interested in the |
| 4 |
> principle of |
| 5 |
> the test :) |
| 6 |
|
| 7 |
I thought you could get then for < $5, but anyway.... |
| 8 |
|
| 9 |
> so I created a file: |
| 10 |
> dd if=/dev/urandom of=Desktop/random.img bs=1024 count=500960 |
| 11 |
> |
| 12 |
> then copied it to the card, and then copied it back as |
| 13 |
> random-2.img. If |
| 14 |
> I md5sum the two files, they are identical: |
| 15 |
> $ md5sum random* |
| 16 |
> 9dcac25cfd8585be5939c0ff969de310 random-2.img |
| 17 |
> 9dcac25cfd8585be5939c0ff969de310 random.img |
| 18 |
> |
| 19 |
> Does that mean my memory card is good to go, or should I use some |
| 20 |
> other |
| 21 |
> method of bad sector detection? |
| 22 |
|
| 23 |
I'd be more or less happy with that methodology, had I copied a |
| 24 |
thousand files to the card & they checked out good. |
| 25 |
|
| 26 |
Of the top of my head I don't know how big your "bs=1024 count=500960" |
| 27 |
file is - I would make a Bash script generate files c 5meg in size |
| 28 |
(maybe alternative between 3meg & 6meg?) and copy them to the card |
| 29 |
until it fills up. Then check them, delete them and do so again until |
| 30 |
all 1000 have been copied & checked. |
| 31 |
|
| 32 |
Personally, I wouldn't be happy with one file being copied & stored |
| 33 |
ok, but I'd probably be happy if the card had proved itself to safely |
| 34 |
store 1000. And 3meg - 6meg is the size of the jpegs taken by my mum's |
| 35 |
camera. I would want to fill up the card, as flash cards try to avoid |
| 36 |
the bad blocks - if you don't fill it, you could be missing some duff |
| 37 |
block every time; once you've filled it you know that all the blocks |
| 38 |
are good. For some values of "good", that is - you don't know about |
| 39 |
longevity, and these cards are really just black boxes to us - we have |
| 40 |
no idea what magic goes on inside. |
| 41 |
|
| 42 |
Personally, for my money, I don't know if I'd trust it. Depends what |
| 43 |
you're storing on it. MP3s for my phone? Sure - I have a backup at |
| 44 |
home. Moving files onto my PS3 or Wii, sure. For my camera? Maybe I'd |
| 45 |
be a bit cautious. |
| 46 |
|
| 47 |
Stroller. |
Archives