On 08/06/2014 10:06 AM, Carlos E. R. wrote:
El 2014-08-06 a las 13:09 +0200, jcsl escribió:
I want to make backup a partition and I want to compress the data. I'm worried about the possibility of the compressed files being damaged when I try to restore then. I've read that in compressed tarball you cannot recover any data after a single damaged bit.
Correct.
Not entirely. It depends on the 'damage'. You need to differentiate between the 'data' and the 'metadata'. You can flip alternate bits in a 'payload' and all you have is a corrupt file. That problem with .taz is that they tar up the files and then compress that resulting .tar file. That is different from compressing each file on the fly and tar'ing the result up into one package. This latter way the metadata is not compressed (or encrypted) and even if one file has flipped-bits they others are let alone. And what if the metadata gets damaged? Well there are tools that scan ahead to see the 'signature' of the next metadata header in a tar file. So its important to think about (a) what you are compressing and (b) the separation of data and metadata. Given that, compressing up the whole .tar file into a .taz does have the risk described by the OP, yes. But it doesn't have to be like that. Think, for a moment, of 'rsync'. It can transmit compressed data but use uncompressed metadata between the source and destination programs. I also recall 'shell archives' (q.v., go google) and it occurs to me that would be a simple way to package compressed data plus clear, tagged metadata in a single file/stream.
I have not ever seen a Linux backup utility that implements both compression and forward data recovery methods - such as used, for example, by pctools backup, back in the 80's, with good results.
Good point. But I wonder if many of those DOS/Windows tools used the separate metadata vs compressed data I spoke of? -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org