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[OM] Re: Deleting in the Camera

Subject: [OM] Re: Deleting in the Camera
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 16 Jan 2007 10:25:27 -0500
Your statement about raw files always being the same size is not 
necessarily true.  I think it's true for the E-1 but definitely not true 
for Canyon raw files which do have some sort of (unspecified but 
presumably lossless) compression applied.  Just looking at the directory 
from my last shoot with the 5D the raw files vary from 10.8MB to 14.8MB. 
  These will obviously not all fit into the same holes in the file 
system allocation table.

You are correct that flash memory bits have a limited life cycle and 
that usage "wear" needs to be distributed amongst the various sectors on 
the card.  However, this is not a worry of the file system.  Wear 
distribution is a function of the flash card and its embedded flash 
controller.  The operating system only worries about specifying a 
certain sector on the disk.  The flash controller will move the physical 
location of that sector to different places in order to automatically 
distribute the wear.  At least I know this to be true for CF cards.  I 
don't know the specifics of other flash card technologies but assume 
they likely do the same.

Chuck Norcutt


Ian Nichols wrote:
> On 16/01/07, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> 
> 
>> If you now take image 6 it will be strung along right after 5 *unless*
>> you've done some editing and deleted image 3.  Depending on the DOS
>> implementation, it might choose to place image 6 right after image 5 or,
>> recognizing that there's a hole where image 3 used to be, it may decide
>> to put image 6 in that empty space.  All is still well if image 6 is
>> able to fit in the hole but, if not, part of image 6 will fill up the
>> hole and the remainder will be placed after image 5.  At this point
>> image 6 is no longer completely recoverable because the recovery utility
>> has no way of knowing that it's missing its tail and, even if it did,
>> has no way of knowing where the tail is.
> 
> This is possibly another argument in favour of always shooting RAW (or
> maybe TIFF).  These are always the same size (er, unless you change
> the picture size... but I'll gloss over that), so image 6 will fit
> exactly in the gap left by deleting image 3.  Then again, filing
> systems aren't always as smart as you think and might put most of
> image 6 in the gap, thinking it's just a little bit too small, then
> put the rest of it someplace else.  Anyone with too much time on their
> hands fancy testing this?
> 
> Come to think of it, a camera will probably fill up the rest of the
> card before going back and filling in the gaps (to avoid excessive
> writing to a particular bit of the card), so it'll probably get filled
> with fragments from the last image recorded because the card capacity
> won't be an exact multiple of the image size,  i.e. there's not quite
> enough room at the end of the storage space for the last image, so the
> first part of it goes there and the rest of it goes into the gap left
> by deletion... then if there are any more gaps, they get filled.
> 
> Yep, I think the KISS principle applies here.
> 
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