At 04:50 PM 2/15/2001 -0500, Prather, Wanda wrote:
>The formula I use is:
>
>Need to back up xxx TB
>Divid by the number of GB that will fit on a tape.
>Adjust as you have suggested for extra versions
>Divide by .65 on the assumption that the not-yet-reclaimed tapes will be, on
>average, 65% full
>Multiply by 2 for the offsite copies
This is pretty close to what I use, too, but make sure you factor in
compression somewhere. Also, if you are using collocation, then you also
need to consider how rapidly your data is changing. If you have high data
turnover, then you will be reclaiming data more frequently. If you don't
have enough tape drives or wall clock time to handle this, you will need
more tapes, plan on a lower average tape utilization, and raise your
reclaim threshold to relieve the pressure on reclaim.
This reclaim issue will not surface at first in a new robot. You will only
run into it over time, after a bunch of your tapes have filled up and you
start doing more reclaims. This issue is also dependent on the tape
technology you are using, as some perform reclaims faster than others.
..Paul
