On 4/25/07, G.T.Smith <[EMAIL PROTECTED]> wrote:
Carlos E. R. wrote:
>
> The Wednesday 2007-04-25 at 11:44 +0100, G.T.Smith wrote:
>
> ...
>
> > The conclusion I am coming too is the the current time stamping
> > mechanism is inadequate for anything but the crudest of time related
> > file management, and possibly not even that given the way some things
> > manage files...
> ....
> > and time stamping was an option...If time stamping was reliable and
> > consistent this could have been used to flag files to backup, it is not
> > so it cant **sigh** I
>
> The modification time can be used to know when to backup the data, and
> the
> change time for the metadata. Meaning, if the modification timestamp has
> not changed, but the change timestamp has, it should mean that the file
> itself it's the same but the attributes have changed, and thus,
> backing up
> of the metadata only should suffice.
>
> In practice, you could compare all metadata: attributes, size,
> dates... if
> any of them changes, backup the file (not optimal). Another method,
> safer,
> is to also store a checksum: if some of the metadata changes (except
> size), calculate the new checksum to see if a backup is needed. For this,
> the metadata of the last backup should be saved on disk.
>
> A good backup program should do all this automatically.
>
I theory good, in practice not.. well look at editor example originally
quoted ... modification time does not always mean content has changed it
merely means the modification time stamp has changed... it would be nice
that everyone handled this time stamping issue in a well defined
manner... in practice many people don't, this is not criticism this is
just an observation BTW
Yes a good backup program will do this ..... but the serious players
would charge me more than the underlying hardware is worth! A couple of
people have pointed me to some stuff on a separate sub-thread which I
intend to look at.. and hopefully I can avoid having to write my own
solution...
Neither of the solutions I posted earlier in this thread are dependent
on timestamps.
iirc: Especially for online backups rdiff-backup mentioned before
ignores timestamps altogether. It calculates the MD5 for every file
to see if any changes have been introduced. If they have it segments
the file and drills down to find the smallest unit of change and only
sends that data across the LAN/WAN.
Greg
--
Greg Freemyer
The Norcross Group
Forensics for the 21st Century
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