On 03/03/2017 07:50 AM, Fred Smith wrote:
On Thu, Mar 02, 2017 at 10:57:51PM -0500, Robert Moskowitz wrote:
On 03/02/2017 10:02 PM, Fred Smith wrote:
On Thu, Mar 02, 2017 at 09:06:52PM -0500, fred roller wrote:
On Thu, Mar 2, 2017 at 8:36 PM, Robert Moskowitz <rgm@xxxxxxxxxxxxxxx>
wrote:
dd if=/dev/sdb of=os.img bs=1M count=3210
I would recommend bs=512 to keep the block sizes the same though not a huge
diff just seems to be happier for some reason and add status=progress if
you would like to monitor how it is doing. Seems the command you have
should work otherwise.
The dd blocksize has nothing to do with the disk sector size.
the disk sector size is the number of bytes in a minimal read/write
operation (because the physical drive can't manipulate anything smaller).
the dd blocksize is merely the number of bytes read/written in a
single read/write operation. (or not bytes, but K, or Kb, or other
depending on the options you use.)
It makes sense for the bs option in dd to be a multiple of the actual
disk block/sector size, but isn't even required. if you did dd with a
block size of, e.g., 27, it would still work, it'd just be stupidly slow.
Kind of wondered about that.
So the blocks reported by fdisk is what I should use as the count,
as that matches the drive's real block size?
thanks
if you're copying the entire device, you do not need to tell it how
many blocks. just use a large-ish blocksize and let 'er rip.
for a single partition, you could use the blocksize and block number
you get from fdisk. you would then need to say /dev/sda4, e.g., instead
of /dev/sda.
when copying an entire drive I tend to use 10M as the blocksize. using
a large blocksize just reduces the number of read operations that are
needed. that's why a very small blocksize could slow down the copy, as
it would require a whole lot more read operations.
Well, I only wanted to copy the used part of the drive which I try to
keep small so I can still copy the image to an mSD card if I wish. So I
have to supply the amount of the drive to copy. The bs=512 went fast
enough, but then I was only copying 3.2GB.
thanks for the help.
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