Image-Based Backup Restoration: How to Recover a Backup to a Disk of a Smaller Size
Scheduled full-system backup is a must in the production environment. If something goes wrong with a system or your computer, you can restore the system to a working state on a working machine and get back to your tasks without downtime. Usually, the recovery process goes smoothly; you just deploy your old system on a destination computer and that’s all. However, there are some use cases that require additional actions.
One such use case is when you need to restore your system to a disk of a smaller size. For example, when you need to move from HDD to SSD, or your alternate computer has a smaller disk (one of our clients’ situation). Below, our system administrator and solution architect explain how to solve this issue when creating an image-based backup in MSP360 Managed Backup Service on Windows OS. All the tools used are Windows built-ins.
Restoring an Image-Based Backup to a Smaller Disk
The data on disk is stored in sectors – the smallest chunks of data on a hard disk. Each file has many sector units assigned to it. These sectors are not located near each other; they can be scattered around the disk. This is called fragmentation, and it is fragmentation that makes it difficult to shrink a partition to the desired size during restore.
It is also necessary to know that the image-based backup plan in Managed Backup Service backs up data by keeping the information about the placement of sectors on the drive, as well as the start offset of disk partitions. Thus, the backup preserves the disk fragmentation as is, with all its inefficiency. If the disk that you’re going to use for system recovery is smaller than the original one, there won’t be enough space for your fragmented system. Here are some measures that will help you to shrink the system before backing it up.
Tip 1. Defragmentation
Defragmentation picks up the file’s fragments and joins them all together, one by one. After it completes, the files in your computer’s storage become sequences of data blocks, and all the blocks that relate to a single file are located near each other. When possible, defragmentation also stocks all the “busy” blocks in a pile, dividing the disk into two parts: one that’s busy with data and one that’s free. Not only does this reduce the size of your system, but it also speeds up your computer. To run defragmentation, open the Start menu and type “defrag”. Windows will show the appropriate option: Defragment and Optimize Drives.
Please note: defragmentation can change the placement of a lot of sectors, even the ones that are for non-fragmented files. In this case, the next block-level backup can grow in size.
However, in most cases, defragmentation is not enough to shrink a volume (but it is worth doing it to start with anyway).
Tip 2. Disabling System Files
There are system files that can be placed anywhere on the system partition, even in the middle of it, regardless of the space used. These files might appear as an obstacle to system shrinking. If the system is working properly, system files can be temporarily disabled. After a successful shrink or restore job, they must be re-enabled. Here is a list of these files:
- Pagefile (pagefile.sys)
- Hibernation (hiberfil.sys) (execute cmd command: powercfg /h off)
- System protection (system restore points)
If you are not sure whether it is worth concerning yourself with system files, you can try to shrink the system disk itself. If the desired size is achieved by performing shrink in a working system, there’s no need to disable system files before running a full backup.
Please note: pagefile.sys is ignored during an image-based backup job; however, it can make it impossible to shrink the partition on a working system before performing a backup.
Tip 3. Lowering Disk Volume
Before starting the image-based backup, shrink the system partition in the source system to the desired size (e.g., to a size that fits your SSD) with the Disk Management tool (open Start menu and type “disk” ) and then perform a full backup. This version of the system will require less space so it will fit the smaller disk.
Deploying Your System
By following these tips, you’ll get a system of the desired size. Now, all that is left to do is to create a bootable USB/ISO in the Managed Backup Service agent. You can find the appropriate option on the Home panel.
When you run the Restore Wizard using your USB or image of the system that you’ve backed up, there will be a step to select the partitions to restore. Here, you will be able to check whether you have done everything right.
Using these tips, you can significantly reduce the size of your system, so that you’ll be able to deploy it on a computer with a smaller disk. Do not forget that all the described actions should be performed before launching the image-based backup plan, otherwise they won’t work. If you have any further questions, please contact our pre-sales team.