[techtalk] RE: backup newbie

[Eric Richard Turner]

On Wed, 29 Nov 2000, Conor Daly wrote:

> but can I do the following?
> 
> 1st of Month:          Full backup
> Sunday:                Differential Backup from Monthly
> Daily:                 Differential Backup from Sunday
> 

Good question. I suspect it depends on the backup utility and/or operating
system. I know that NTBACKUP on Windows NT uses the archive bit on each
file. During a full-system backup it clears the archive bit on all files.
When a file is changed, the archive bit is set. Differential and
incremental backups save only those files for which the archive bit is
set. The difference between the two is that during differential backups,
the archive bit is not cleared whereas during incremental backups the
archive bit is cleared.

So, using NTBACKUP on Windows NT, the answer to your question is no.
However, it seems reasonable that one could write a backup utility that
would catalogue when each file has been saved, perhaps using a checksum,
CRC or last-modified date to determine when a file has been modified. Then
the backup utility could do all sorts of interesting backup scenarios
based on the combination of the catalogue and the list of modified files.
Whether or not this sort of thing exists is beyond the scope of my
experience. I've never had to set up incremental or differential backups
for Linux, so I'm not sure what can and cannot be done. I recently
received the latest Linux Journal, which has an article in it about
automated backups in Linux. Now I'm curious, so I guess I'll just have to
read it :-)

Eric R. Turner


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