8 Mar
2013
8 Mar
'13
5:40 a.m.
On Mar 8, 2013, at 1:29 AM, Chuck Guzis <cclist at sydex.com> wrote:
On 03/06/2013 07:25 PM, Roe Peterson wrote:
Logical blocks, yes. But AFAIK, it has no capability to reproduce the size of physical
blocks when doing a tape-to-disk transfer. How could it? Unix has no way to specify the
size of variable-sized physical blocks on disk.
True, but going in the other direction, blocking factor is preserved in variable
sized writes to tape. For example, if I write a series of 1k blocks to a tape, and try to
read them back as 2k blocks, each read will return only 1024 bytes, at least on
streaming-type tapes. I'm not sure what would happen on real magtape.
So,writing a tape with dd will, by default, create 512-byte blocks.
dd
doesn't change blocking, it's just a byte-by-byte dump, unless
you specify otherwise. Tar, on the other hand, looks for files.
Actually, dd uses 512-byte blocks by default,and always has. At least
since V6, anyway... --Chuck