Subject: Re: Amanda backups: gtar or dump?
To: Curt Sampson <>
From: Simon Burge <>
List: current-users
Date: 10/28/1998 10:02:28
On Tue, 27 Oct 1998 10:01:41 -0800 (PST)  Curt Sampson wrote:

> Actually, one of my main complaitnts about dump is there doesn't
> appear to be a way to verify the integrity of a dump, and it doesn't
> even appear to do checksums on the files. That's why I've been
> using Gnu cpio with the -H crc option for so long. (It's still
> irritating that it doesn't check the crc when it lists, though;
> you have to do an actual extract to do that.)
> Personally, I'd switch to dump in a flash if a) it did a checksum
> or CRC of each file, and stored it in the dump file, and b) it
> checked this and generated a message on mismatch when you did a
> restore -t.

Maybe storing a checksum in the di_spare field of the inode is a
solution to this.  Two problems with this are: 

 * The inode gets written before the data so you'd have to read all data
   of the disk twice.  You'd then still have a dump tape that older
   versions of restore could handle.  The other option is to add a small
   record after the file's data containing it checksum, but then you
   have an incompatible tape format.
 * If the file changes the checksum will be invalid.  This could be a
   useful feature though, not a bug!

An ulgy idea is to store the file's checksum in the _next_ file's inode
data, and have a dummy inode at the end of the tape with the last file's
checksum in it.

Sound good, bad or otherwise?