How to estimate your real backup requirements
Most backups involve just backing up ALL the disk storage your site has. This is both costly and wasteful. On the surface it may seem to be the quick and easy way to cover everything, but in reality it creates a monster, that more often than not, fails to provide the required protection.
First, it is very important to understand the three very different problems backups are used to solve.
1. System failure: the hardware fails and you lose all the information on it, or the database crashed and will not recover.
2. “User error,” I deleted a file last week I really need, or plans changed and I need to “undo” two weeks worth of work.
3. Audit requirements: we need to produce the accounting month end supporting files for 4/1999.
Each of these problems have very different requirements for the backups that are needed to correct them.
1. System failure, a full backup from the last stable point immediately before the error is perfect. The best strategy is to have a “ghost” copy of the base system, and one or maybe two copies frequently overwritten with the latest set of files needed to bring the “ghost” current. There is no value in being able to go back farther than the last “clean” state.
2. User errors require multiple layers of copies going back one or two business cycles. Only the files the users save or provide input to need to be saved. One scenario might be: one copy from last night and four weekly copies.
3. The third type is normally the easiest, as it is dictated by the audit requirements. There are two subtypes here. First: backing up of a running journal or log, this needs to be the same as the system backup above. Second: the backup of a “close” or other accounting point, this type of backup needs to be manual and is normally part of the “close” process. It will also need to be kept on a schedule based on the record keeping requirements.
Determining your needs:
1. Start with the first problem, system failure.
· Given you have your original install disks what set of files would you need to recover your system,
and what is their total size? _______Mbytes (1a).
· How much does this number grow each month? _______Mbytes (1b).
· On the average, how many files are created, modified, or saved each day? ______
· What is the total size of these changed files? _______Mbytes (1c).
2. What is the approximate cost of losing your work for?
· 1 day ______
· 1 week ______
· 1 month ______
· The whole system _________
3. What is the total size of the storage you are currently using?
· Total amount of PC disk storage. ________Mbytes.
· Total amount of server storage used ________Mbytes.
· Approximately what percentage is duplicated? ____% (3a)
IE. Identical files found on each PC (Windows, Applications, Etc).
4. For the second and third problems, you need to look at your business cycles.
· When do you sum up and “close”: Daily, Monthly, Quarterly and/or Yearly.
· How many copies of “work in progress” are required? ______
· At what interval should these copies be kept? ______
5. What backup schema is right for you.
· _____ Daily copies.
· _____ Monthly copies.
· _____ Quarterly copies.
· _____ Yearly copies.
· _____ ______________ copies.
· _____ Total number of copies (5a).
Sizing the Server:
Now use total space from (1a) + 12 * (1b) above ______Gbytes.
Add to that 100 – (3a) percent of (5a) * (1b) ______Gbytes.
Total protected storage required ______Gbytes.
If you have difficulty answering the above questions, we have consulting services and tools that can help.