Accidentally used mkfs.ext4 on Microsoft Reserved Partition while installing Arch Linux

Question

The title says all. Windows still boots, but I'm afraid of any future errors. How to fix this?

Operating System:Windows 8.1

Below is the output of parted print if it's helpful.

Disk /dev/sda: 1000GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name                          Flags
 1      1049kB  420MB   419MB   ntfs            Basic data partition          hidden, diag
 2      420MB   693MB   273MB   fat32           EFI system partition          boot, esp
 3      693MB   827MB   134MB   ext4            Microsoft reserved partition  msftres
 4      827MB   179GB   179GB   ntfs            Basic data partition          msftdata
 7      179GB   190GB   10.7GB  ext4
 8      190GB   203GB   12.9GB  linux-swap(v1)
 9      203GB   268GB   64.4GB  ext4
 5      351GB   980GB   629GB   ntfs            Basic data partition          msftdata
 6      980GB   1000GB  20.1GB  ntfs            Basic data partition          hidden, msftdata

Answer 1

The Microsoft Reserved Partition is not used at 100% of the time from the operating system, which allows you to boot Windows and use it. It might however cause issues in the future, like boot problems and system update problems. It will be good if you manage to fix it.

There are several ways of restoring it and I'll copy one (I haven't tested it myself!):

Rebuild or repair (deleted) system reserved partition via cmd (command prompt)

1. Boot computer with Windows 10/8/7 installation media and press Shift + F10

2. Run the following commands at the command prompt:

   bootrec /fixmbr  
   

   If you receive the error message “Element not found”, you may need to mark the boot partition as active with diskpart beforehand.

3. Enter below commands at the command prompt:

   diskpart
   select disk 0
   list partition
   select partition #
   

   Note: Select the "System Reserved" partition (if you have it) or the Windows OS partition.

   active
   exit
   

4. Type: bootrec /fixboot and press Enter in the command prompt.

5. Type: bootrec /rebuildbcd and press Enter in the command prompt.

After these steps, you can reboot the PC and continue to use your computer again, and the deleted system reserved partition will be restored.

The source I have used for this example is this one.