Problems while reading from /dev/cd0

Dimitry Andric dim at FreeBSD.org
Tue Aug 23 11:12:56 UTC 2016


On 23 Aug 2016, at 08:50, Gerhard Schmidt <estartu at ze.tum.de> wrote:
> 
> I'm having some very curios Problems while reading from an BD-R recorded
> as a tar directly on the disk without a filesystem.
> 
> When i try to read the Disk via 'tar tvvf /dev/cd0'
> 
> i get the following output
> 
> -rw-r--r--  0 root   wheel 5793264611  1 Jan  2015 file1.db
> tar: Error reading '/dev/cd0'
> Archive Format: POSIX ustar format,  Compression: none
> tar: Error exit delayed from previous errors.
> 
> reading the whole file via 'dd if=/dev/cd0 of=backup.tar bs=2048' and
> than 'tar tvvf backup.tar' the file is read without a hitch. So the data
> on the disk is OK but can't be read directly by tar.
> 
> if i try the dd without the bs=2048 i get
> 
> dd: /dev/cd0: Invalid argument
> 0+0 records in
> 0+0 records out
> 0 bytes transferred in 0.000115 secs (0 bytes/sec)
> 
> So there is a problem reading anything other than 2048 byte blocks from
> a Disk.

Have you tried tar's -b option, to set the block size 2048?  Maybe that
will help.

-Dimitry

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