Differential 1st Backup Question
So I am going to try my first differential backup and had a question (normally I have only done new full backups.) Last month I made a full backup with normal compression of a 2TB external hard drive. For the sake of this question let's assume that the 2TB drive contained files both large and small that totaled approx. 1.6TBs. After a month I have added and deleted files. Let's assume that the 2TB dive now stands at say either 1.5TB or 1.7TB full. Can anyone suggest a ball park figure on how large this first differential backup will be obviously taking into consideration the addition and deletions. Unless I misunderstand how differential backups work this "differential image" should be quite small since it will only reflect the changes made to the initial full backup. Do I have that right? TIA.
Bobbo_3C0X1 wrote:That's correct - mostly :)
Unfortunately, there's no way to know exactly what changed though. For instance, if you deleted 200GB of data and added 201GB of new data and then a differential kicked off, even though there is only 1GB difference in size noticed in Windows, you'd actually be backing up 201GB of changes in each subsequent differential plus any additional changes on top of those between the original full and each differential afterwards.
But under regular case usage (you delete some, you add some, but only a couple GB at a time), then yeah, your Diff changes shouldn't be too bad.
Also, FYI... video files, graphic files and things of that nature are already compressed. So, if those are the primary file types changing, then your differential sizes will be close to the actual amount of those file type sizes. Acronis can't really compress files more when they're already in a compressed format.
Thanks for the response.
>That's correct - mostly :)
Ugh : ) I hate caveats. I imaged 4 2TB external drives onto an 8TB external drive and that left me with about 800GB or so of room left on the 8TB drive. I was (am) hoping that when I attempt to make differential backups for the first time of all 4 2TB drives onto the 8TB drive it will be easy peasy with small differential backups. Whaddya think the chances of that happening are : )
I think your chances are good. In your scenario in the OP you seem to be working with 0.2TB spread of data or around 200GB in changes. If that holds true then you should have room to work with. It might be advantages for you to increase the number of times per month you make backups. I have found that the longer you wait to run an INC or DIFF backup the larger they are.
I agree with Enchantech. You should have some room for differentials to add on. You'll likely run out of room if you have a cleanup schedule though, as it will want to create a new full, before any of the old files can be deleted.
Ideally, you might want to split them onto 2 disks if you plan to do that (as the differential sizes will grow over time and you'll be accumulating them as well without cleanup). For the interim, you should be OK though. You might start to see performance issues on the 8TB drive if you start getting below 10-15% of free available space.