How Much Space do I need for My Backups?

Dennis Faas's picture

Infopackets Reader Eric H. writes:

" Dear Dennis,

I just read your article on 'Why You Should Install KB3000850?', in which you mentioned doing daily operating system backups. I have a question about disk images. I have used Norton Ghost (disk image backups) on my old Windows XP system many years ago and I stored my backups on a 250GB external drive.

Now I have a 250GB Samsung Solid State Hard Drive (SSD) and a 2TB hard drive for my other data. My question is, how much space do I need for my backups? As I understand it, incremental backups will only copy over any changes that it finds are different then previous backup. Can you shed some light on this? "

My response:

How much backup space you need for backups depends on how big the hard drive is that you wish to backup, and how much data is stored on that drive. The general rule of thumb is that an operating system (OS) hard drive will compress approximately 50%, providing that you have maximum compression enabled in your backup program. So, if your 250GB drive was 1/2 full of data (125GB) and you backed it up with maximum compression enabled, the backup set would be roughly 60GB. But that's only for one backup set; you should have many more backup sets available at all times, in case one fails.

Incremental Backups and Refreshing Archive Sets

Incremental backups work like this: the first backup run is the 'main backup' set. Any changes you make to your PC after the main backup is run are considered as 'new' data. The next time your backup runs, only the new data is added onto the main backup set.

I recommend you have a rotating schedule in place such that your incremental set is reset / renewed every week or two. The reasoning is that sometimes incremental sets can become corrupted, which means that you may not be able to restore all or part of your incremental backup set. Resetting your backups every week or two would give you a new archive set to work from.

How Much Space do I need for My Backups?

As I mentioned previously, how much backup space you need for backups depends on how big the hard drive is that you wish to backup, and how much data is stored on that drive.

Let's use your operating system drive as a backup example. Assuming that your operating system is stored on the 250GB SSD hard drive, I recommend you backup that drive every other day and utilize incremental backups to save space on backups on the destination drive (in your case, the 2TB drive); you would then refresh the archive set every two weeks. Let the backup run on schedule for 4 weeks to get an estimate as to how much space is being used in your backups. Then, create an auto-pruning schedule whereby your old backups get deleted automatically. If you use Acronis True Image, all of these options are available to you.

If you require further assistance, I can set up your backups for you using remote desktop support.

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About the author: Dennis Faas is the owner and operator of With over 30 years of computing experience, Dennis' areas of expertise are a broad range and include PC hardware, Microsoft Windows, Linux, network administration, and virtualization. Dennis holds a Bachelors degree in Computer Science (1999) and has authored 6 books on the topics of MS Windows and PC Security. If you like the advice you received on this page, please up-vote / Like this page and share it with friends. For technical support inquiries, Dennis can be reached via Live chat online this site using the Zopim Chat service (currently located at the bottom left of the screen); optionally, you can contact Dennis through the website contact form.

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Tessman_Ian's picture

my system refuses to start Windows when it fails, and everythin I've tried to use requires a recovery disk to restore the system. It takes a very long time to restore my system drive. My system files are about 40GB. Isn't there a backup program that would allow me to boot from a CD or USB recovery media and restore my system drive faster? I back up to an internal drive dedicated to backups.

Dennis Faas's picture

If you used a program like Acronis True Image you could build bootable rescue media CD / USB and then restore backups that way. I personally have a C drive dedicated to Windows only and then store everything on D drive (same hard drive, two partitions). If anything goes wrong with Windows, I can restore C without having to restore D (my data files). I then backup everything onto my server which is on another PC on the same network using incremental backups similar to how I described in this article.

Greg1956's picture

Hi Ian,

I've been using Easeus Todo Backup Free for about 5yrs, and backup from my C drive (Windows and programs) to a separate drive (G) within the PC

I've created a Rescue disc from Todo Backup and I've used it once when my PC was infected with malware.

I also copy this backup to my network server once a month.

So my procedure is to backup once a month to drive G and my server


Tessman_Ian's picture

My system architecture is basically very simple. I have a SSD dedicated to my OS, Windows 7, system drive C. I've mapped my documents in use to a separate Drive, which I backup routinely to an external drive. I configured it this way to minimize the size of my System drive. Any files stored in my Libraries Are backed up routinely to an external drive. Everything I backup to external drives are simple file copies. I configured it this way deliberately to minimize my System drive, and to be able to use my documents on a different machine easily. My System drive is less that 40 GB.

In spite of this, when I've had to restore my system, it is S L O W.

Both Acronis and Ease-US require a rescue disk which appear to be basically the Win 7 boot disk choosing the option to solve a start up repair. Is this the best that is available?

Thanks for any advise


Greg1956's picture

Hi Ian,

if you mean Restoration takes a long time , I agree

I have a 120Gb SSD for Win7 and D,E,F,G drives for programs, data and backups

120Gb backup takes 15minutes to create and about 2hours to restore from backup.
Not sure why it takes so long, but I was just glad to have it back.

BTW it was from my G (250gb WD) , it could be faster if it was from another SSD but that is just my speculation. SSD is at least 5x faster than my other HDDs