[wellylug] DD no go

[Cliff Pratt]

David Antliff wrote:
> On Sat, Apr 5, 2008 at 11:37 AM, Cliff Pratt <enkidu at cliffp.com> wrote:
>>  > Thirdly, there's nothing special that comes to mind about the number
>>  > 4298739712, in case you were wondering.
>>  >
>>  It's pretty close to 4GB which is a FAT32 filesystem limit. Or is it?
>>  I'm fairly sure there are a number of limits, 2GB being one of them.
> 
> But... but... /dev/sdb is a disk device... he's not writing to a file
> *ON* a FAT32 filesystem, he's writing to a block device that just
> happens to contain a (new) FAT32 filesystem, and he's nuking it by
> writing there...
>
True.
 >
> As far as dd is concerned, whatever is on sdb is irrelevant. It's just
> going to overwrite it. The same would apply if he was writing to
> partition sdb1 containing a FAT32 filesystem - it will simply
> overwrite it. Where this *would* apply is if he had created a FAT32
> filesystem on partition /dev/sdb1 and mounted it at, say, /mnt/blah
> and he was trying to dd of=/mnt/blah/myfile.
> 
> /dev/sdb and /dev/sdb1 (and all other 'disk' devices) are just block
> devices - filesystems make no sense here, they are data structures
> stored ON a block device.
> 
> It's very unusual to create a filesystem on a disk device. It's far
> more common to partition the disk device into multiple partitions and
> then create a filesystem on one of those. I'm not even sure what
> happens if you try and create a filesystem on a disk device and mount
> it. Should work I suppose? Unusual though.
> 
As regards filesystems on devices, don't floppy disks work that way? And 
CDs/DVDs and USB keys? (I could be wrong!)

Cheers,

Cliff