Hi James,
In my experience, the most often restore of a file from backup is from
yesterday's tape.
Then it reduces from there.
It is also a simple question of what the business wants.
Some places I've worked for wanted a backup of everything and were
prepared to pay for it.
Others were only interested in restoring from the previous month and
then a monthly tape from before that.
So, check with the owner what they want. Give them options of
cost/backup options. Let them decide what they want.
Then it's not your problem on how long backups are retained. You then
only have to make sure you live up to what is wanted.
Ben
On 22/08/2010 4:54 PM, james wrote:
G'day guys
I've spent many hours with pencil and paper, I certain, but am asking in case
someone older-n-wiser can offer sage words:
If I want to backup a system for n days, and be able to recover any particular
days files the only way that I can see is to have a daily backup for n days.
Tower of Hanoi (for eg) says you can backup 2^^n-1 days with n tapes but i can
break that. Simple EG starting with day 4 sequence ie backup:
C A B A C A B A (http://en.wikipedia.org/wiki/Backup_rotation_scheme)
On day 2 you create a file, which you remove on day 3. On day 6 you try to
restore day 2 ....
On day 6 you have:
A from day 5
B from day 2 (or worse from day 6)
C from day 4
So the file created on day 2 backed up on day 3 is lost.
Can anybody point to the boat (I've missed) or confirm my vision.
Thanks
James
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