Looking for a bit of advise. My company currently runs weekly full backups (weekend) to tape and daily incrementals to disc. Recently we have been having drive space issues that I suspect tweaking my backup policies can resolve.
In regards to my incrementals, one issue I have is that every night I perform my incrementals with a 24 hour overwrite protection. The issue with this is that my incrementals will start being overwritten before the next full is completed due to the 24 hour overwrite protection. If I set the overwrite protection to 4 days, then every day but the first incremental backup will expire after the next full backup thus taking up disc space unnecessarily. The only two things I can think of to resolve this issue is to either make a media set for every weekday,
media set ---- overwrite protection
Monday ---- 4 days
Tuesday --- 3 days
Wednesday -- 2 days
Thursday -- 1 day
This seems a bit combersome.
Switch to differentials and just set to overwrite everynight. In this case, my understanding it is that it will backup all changes since the last full every night. This equates to a lot of redundant backups but the overwrite protection is much more manageable.
I am hoping that there my be functionality or options I am not thinking of here and would like any suggestions/comments that there may be.
Could you possibly expand as to why this would not work?
"Switch to differentials and just set to overwrite everynight. In this case, my understanding it is that it will backup all changes since the last full every night. This equates to a lot of redundant backups but the overwrite protection is much more manageable."
Granted, the differential would grow every night but there would only be one backup per week which will be overwritten each night. This option allows me to only need one media set.
I also don't see how setting my OPP to 4 days would do anything but compound the issue, since it will retain incrementals several days after the full is completed.
Even though I don't really like the 4 media set idea, I don't see why that wouldn't work as well.
As I see it: (and I may be wrong)
The amount of disk you would use is the same
Day1+Day2+Day3+Day4+Day5 = total GB used on disk
100+100+100+100+100 = 500GB
Day1 = 100GB used on disk
Day2 = 200GB used on disk
Day3 = 300GB used on disk
Day4 = 400GB used on disk
Day 5 = 500GB used on disk
the only difference is the number of backup sets on disk
Incrementals give you a better chance of recovering a file that changes every day as you have up to 5 versions of it. With differentals you have only 1
I am talking about your first scheme with the decreasing OPP. In terms of disk space, it is the same as setting the OPP to 4 days. At the end of the week, you still end up with 4 incremental backups.
You can use differential backups to minimise your space usage. If you do use differential backups, keep at least 2 copies of backup on disk, so that when you overwrite one of them you still have the previous backup to fall back on. Otherwise, if your Thursday differential backup fails, you would only have your full backup to fall back on.
The other thing to consider when you use differential backups and do not keep a lot of copies: You would not have the ability to restore a version which is overwritten. For example, you keep 2 copies of differential backups. On Friday, you would have the differential backup for Wed and Thu. Suppose you have a file which is modified every day and you need to restore a version of it as of end-of-business on Tue., you would not be able to do so.
Disk is cheap nowadays. Rather than wasting time trying to work around the lack of space, it is probably more productive to get more disk space.