Not quite. My comments within ...

> I have a client that will be backing up a data set which:
>
> 1) The client needs a full backup every 90 days with incrementals 
> backups in between on a 1 year retention policy.
>

In my limited experience, 90 days is an unrealistically long expectation
for frequency of full NetBackup backups. You may schedule this, but I
think you'll find that occasionally your incrementals will start backing
up everything and you'll need a new full. Maybe this has been fixed
recently or maybe all my occurrences have been user error?

> I explained to the client that doing differential-incrementals would 
> be a nightmare to do a full restore.
>

Assuming anything changes, ... yes!

> I then continued to explain that cumulative-incrementals would use a 
> lot of tapes.
>

Not necessarily.

> I suggested the following:
>
> *Day 0: Perform full backup.*
>
> Day 1: Perform differential-incremental.
>
> Day 2: Perform differential-incremental.
>
> Day 3: Perform differential-incremental.
>
> Day 4: Perform differential-incremental.
>
> Day 5: Perform differential-incremental.
>
> Day 6: Perform differential-incremental.
>
> *Day 7: Perform cumulative-incremental. ****
>
> Day 8: Perform differential-incremental.
>
> ...
>
> Suppose at the end of the month the client wanted a FULL restoration 
> of all files, by using this method tell me if this is correct:
>
> 1) Restore Day 0?s full backup.
>
> 2) Restore the cumulative backup from Day7, Day14, Day21,Day28.
>

No. The cumulative incrementals are based on the latest full.

> 3) Restore the differential-incremental backups from Day29,30,31.
>
> Then I would have fully restored all of the files, correct?
>

Again, it would help to know the data better. If files come and go,
having a policy with "True Image Restore" and "with move detection" will
be critical. Otherwise, some files may not be backed up until the next
full and some files will be restored that didn't exist at the Day 31 backup.

> Please let me know if this makes sense.
>

Not as described. Are the full backups so problematic that they must be
scheduled so far apart? I think a month is too long between full
backups, in most cases. What if your most recent full backup is
defective? What have you lost and how would you recover?

If you know a bit about your data, how it is expected to change, and
your backup infrastructure, you should be able to estimate the costs of
this and other setups.

To my mind, you want backup and recovery to be dirt simple, because when
things go wrong, you want simple, fast recovery and when things go wrong
with the recovery, you want alternatives.

Hope this helps! cheers, wayne