ADSM-L

[no subject]

2015-10-04 17:30:26
=3D> On Tue, 2 May 2000 07:35:43 +0200, sal Salak Juraj =
<sal AT KEBA.CO DOT AT> said:

> Allen,

>> There is simply no technical reason to prefer a full/incremental =
scheme
...

> There is one reason for not to go with incremental backup: the =
restore
> speed.  Due to its very nature, the restore speed will be slower =
comparing
> to restore from full backups. (when both use same tape HW) Depending =
on
your
> requirements an environmenmt this limitation does not necessarilly =
have
to,
> but do can apply.

> best regards


I'm sorry, but I must respectfully disagree with you.  In fact, a
well-managed incrementals-forever scheme in a system like ADSM can be =
faster
than a full/incremental scheme.  Consider:

On any day except the day the full was taken, you must mount a minimum =
of
two
tapes to complete a restore.

A TSM stgpool with colocation active (and adequate media levels) will =
only
need a single mount, unless there is more than one tape's worth of =
data.

There are of course variables in either scheme:

If you're using "true incrementals", i.e. only backing up files changed
since
the last _backup_ instead of since the last _full_, you can require a =
whole
weeks' tapes.

You could have your data on a mostly-reclaimable tape, in which case =
you
might
need a second mount.

etc. etc. etc.

But in any case, a well-implemented storage managment system will be =
better
than the average case for a full/incremental scheme, and will be much =
better
than the worst case.


Allen S. Rout
NERDC TSM admin
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