# Thread: Backup Storage Disk Space Calculator

1. ## Backup Storage Disk Space Calculator

I am attempting to build myself a calculator that will help me estimate how much backup storage (hardware) I will need depending on the type of retention I assign to my backup jobs.

In other words, I have the following as a base sample. Depending on how I change the values, I'd like to develop some formulas to help me tell the bosses what kind of future investment they are looking at financially for backup storage.

Initial Data size: 10TB
Deduplication ratio (estimate on duplicate data): 50%
Incremental backups: 500GB DAILY
Daily Backup Retention: 30 days
Weekly Backup Retention: 4 Weeks
Monthly Backup Retention: 12 Months
Yearly Backup Retention: 7 Years

So my thinking on the formulas is as follows:
A = [Initial data - (Initial Data * Deduplication ratio) + Incremental backups]
B = Daily Backups
C = Weekly Backup
D = Monthly Backup
E = Yearly Backup

[[A*B] + [A*C] + [A*D} = [A*E]]

When I tried various formulas for the above, I did not account for the progressive nature of the data. As in, naturally some data will age off while the 500GB will grow. Overall, I'm just trying to estimate but I do need to account for the above and it seems to be above my excel skills in designing the formula.

Any assistance is appreciated.

Thanks.

2. I believe you'll find some good help at the following web site: http://www.backupcentral.com

Curtis Preston, the director of Backup Central, is a master craftsman on all sorts of backup issues. And, just like at Windows Secrets forums, you'll find many other masters hanging out at the Backup Central forums who know everything there is to know about backups.

3. Appreciate it! Already a member and this is actually a discussion a lot of us have on the forums since the majority of discussions seem to revolve around various backup software technologies. I don't really have a choice in that but do want to be able to ballpark how much storage I'm going to need, regardless of the software the company chooses to use.

Thanks.

4. This is an oversimplication and is alot what you have but I see it at any instant of time you have 30 Incremental Backups of 500 GB = 30*500/1024 ~15 TB. I would presume (as you seem to from your formulas) that there is no deduplication of this data.

At any instance the total number of Full backups will be 4 Weekly + 12 Monthly + 7 Yearly = 23 total Full Backups. If we presume that a "typical" (or most probable) is 10 TB [Change as desired] the total amount in Full Backup will be 23*10 = 230 TB. If we presume 50% deduplication in the backup then there is 230*(1-50%) = 115 TB in full backup.

This means a total of 15 + 115 = 130 TB needed.

The question you raise about the changing nature of the data would have to be simulated in some manner (or just based on modeling typical usage perhaps). You don't provide enough information to model or simulate anything other than the 130 TB estimate.

Steve

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