>>>>> On Thu, 2 Jun 2011 11:10:32 +0200, Ralf Gross said:
>
> I always thought that a VolumeToCatalog job would not read the
> data written to the volume and calculate the md5sum again. Instead it
> would just read the file attributes that were written to the volume and
> compare that with the attributes in the catalog.
>
> At least the volume format described in developers.pdf suggest that the md5sum
> information is part of the data stream.
>
> 10.7 Record Header
>
> #define STREAM_UNIX_ATTRIBUTES 1 /* Generic Unix attributes */
> #define STREAM_FILE_DATA 2 /* Standard uncompressed data */
> #define STREAM_MD5_SIGNATURE 3 /* MD5 signature for the file */
> #define STREAM_GZIP_DATA 4 /* GZip compressed file data */
> /* Extended Unix attributes with Win32 Extended data. Deprecated. */
> #define STREAM_UNIX_ATTRIBUTES_EX 5 /* Extended Unix attr for Win32 EX */
> #define STREAM_SPARSE_DATA 6 /* Sparse data stream */
> #define STREAM_SPARSE_GZIP_DATA 7
> #define STREAM_PROGRAM_NAMES 8 /* program names for program data */
> #define STREAM_PROGRAM_DATA 9 /* Data needing program */
> #define STREAM_SHA1_SIGNATURE 10 /* SHA1 signature for the file */
> #define STREAM_WIN32_DATA 11 /* Win32 BackupRead data */
> #define STREAM_WIN32_GZIP_DATA 12 /* Gzipped Win32 BackupRead data */
> #define STREAM_MACOS_FORK_DATA 13 /* Mac resource fork */
> #define STREAM_HFSPLUS_ATTRIBUTES 14 /* Mac OS extra attributes */
> #define STREAM_UNIX_ATTRIBUTES_ACCESS_ACL 15 /* Standard ACL attributes on UNIX */
> #define STREAM_UNIX_ATTRIBUTES_DEFAULT_ACL 16 /* Default ACL attributes on UNIX */
>
>
>
> So I think that only the md5sums on the volume are compared with the md5sums in
> the catalog. If the file data on the volume was damaged somehow this could not
> be detected.

It defintely doesn't recalculate the md5sums from the data streams, but it
does check the crc of every block so it should detect corruption at that
level.  It also checks that the catalog and volume contain the same list of
files.

__Martin

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