Back to the Future with Backup Image Expiration Dates
We've been getting a lot of questions lately about ways that Backup Reporter can report on things in the future. There are lots of ways to do forecasting but one of the best ways to look in to the future has to do with backup media retention. As you know when NetBackup does a backup it stores a date and time that the backup will expire. When the backup is expired that space on disk or tape is available to be written to again. Setting retention levels is a common way to decide how far back you can restore data but as the environment you are protecting grows so does the amount you need to spend on disk or tape to keep up. At some point someone usually says "hey we're spending too much on tapes (or disk space)". Rather than spending money on buying more perhaps we can see what will become available or expired in the future and more accurately predict what can be reused. Let’s say by way of example that you do about 100GB of backups a month. It’s the end of March tomorrow and your cabinet of tapes is almost empty. We may not need to buy tapes if we have 100GB worth of tapes expiring next month so using Backup Reporter here is a report that shows the amount of space becoming available (or expiring) each month for the next 3 months:
It’s segmented by nice bright colors to show how much of each tape type (DLT, HCART, 8MM etc) will be available each month as well. So with our example we may only need to buy a few tapes to make up the 10GB difference needed for the next month since about 90GB will be coming available. Of course, keep in mind that this is for the whole month so if the 90GB that is freed up doesn’t expire until the end of the month it won’t help a whole lot at the beginning when you need it. You could run a more detailed report that shows the grouping by week or day rather than month to answer that question. In general this report is meant to give you an idea of how much data you will be “getting back” each month.
The other way you could look at this is by number of tapes. Doing that same report but tweaking the Y-axis to be number of tapes instead of amount of space yields this report:
This is useful since it shows the number of tapes of each type coming back onsite. Modifying the example of needing to do 100GB of backups next month, say you know instead that you need to buy 1,000 tapes. Based on this report you will be getting back nearly 2,000 tapes so you could perhaps delay that purchase. Again, the caveat that you may need to break it down further by week or day instead of month to make sure you have enough available at the beginning of the month.
All of these types of reports are great ways to slice backup media expiration dates and retention levels. If you’re planning to attend Vision this year we’ll be presenting a paper and discussing ways of putting these reports together to do just-in-time inventory analysis. Using this technique you can do away with keeping unused tapes or disk space around since you’ll know exactly how much space you’ll need and when you’ll need it.