What is being described here is not an incremental backup but a differential
backup.

Incremental backups reset the archive bit. Differential backups do not.

Incremental backups backup files that have changed since the most recent
backup, be it a full or another incremental.

Differential backups backup files that have changed since the last full
backup.

The difference is that to do a restore on an incremental you need to restore
the full backup then each of the incremental backups. To restore a
differential backup you restore the full backu and only the latest of the
differential backups. There are advantages and disadvantages to both methods,
mostly on the time it takes to do the restores and the backups at the end of
the sequences.

 >  JS> It does if you overwrite the original incremental back up each day.  A
 >  JS> standard back-up routine is to do a full back-up once per week, and an
 >  JS> incremental daily, overwriting the incremenatal each day, so it
 >  JS> contains only files that changed or were created since the last full
 >  JS> back-up.  This is essentially what you are doing, and is what the
 >  JS> archive bit on files is used for.

 >  LE> ARGGHHH! NO!

 > ARGGHHH! YES!

 >  LE> The "standard" scheme you refer to requyires a *seperate*
 >  LE> incremental backup tape for *each day*.

 > Nope, it doesn't.

 >  LE> Doing it the way you just described woud have a file get
 >  LE> created on Monday, included on monday's incremental backup,
 >  LE> and *not* included on Tuesday's backup because it hadn't
 >  LE> changed on Tuesday. So if you were using the same tape for
 >  LE> monday and tuesday, you'd no longer have the file backed up.

 > Note quite.  Doing it the way I discribed does not change the archive
 > bit, which is your choice when you do backups with RAR or PKZIP.  You
 > change the archive bit on full back-ups, on daily incremental backups
 > you don't reset the archive bit, so each day you get all changed files
 > since the last full backup, and files that are no longer on the drive
 > are gone, which is what the original poster wanted to happen, and also
 > how I want it to happen, and is how I've been doing it for years,
 > including when I did tape back-ups.

 >  LE> This is because the archive bits get cleared by *either*
 >  LE> sort of backup.

"Either" implies two types of backup. There are really 3: full, incremental
and differential. Full and incremental clear the archive bits. Differential
does not. Full backups all files. Incremental and differential backup only
files that have the archive bit set.

Bert

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