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I accidentally managed to delete MSR partition on one of my (3TB - GPT) data storage drives during Windows installation. Windows still sees the drive and all files inside. I backed up everything just in case, but now I am wondering whether I should try to restore this partition or not.

According some MS help articles MSR is required even on secondary drives - but is it? By the looks of it drive is performing very well and no data has been lost (yet). From gronostajs answer deleting this partition shouldn't cause any issues now, but some may arise in future (but what kind of issues)?

It's a placeholder invented by Microsoft. It doesn't contain any meaningful data and it's there just in case you'd ever need to create some additional partition for special uses. In that case, Windows will shrink the Reserved partition and create a new one in the recovered place. Deleting it shouldn't do any harm now, but you may face some problems in the future.

From what I understand, MSR is used for things like Bitlocker, but I don't really use this feature.

Thanks for answers

EDIT: I just ran cre par msr in diskpart. It created new MSR partition, I don't know if it's all that's needed to restore it to state before I accidentally removed this partition. Guess I'll hope for the best something won't mess up :)

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This is the information from Microsoft.

What is a Microsoft Reserved Partition (MSR)?

The Microsoft Reserved Partition (MSR) reserves space on each disk drive for subsequent use by operating system software. GPT disks do not allow hidden sectors. Software components that formerly used hidden sectors now allocate portions of the MSR for component-specific partitions. For example, converting a basic disk to a dynamic disk causes the MSR on that disk to be reduced in size and a newly created partition holds the dynamic disk database. The MSR has the Partition GUID:

DEFINE_GUID (PARTITION_MSFT_RESERVED_GUID, 0xE3C9E316L, 0x0B5C, 0x4DB8, 0x81, 0x7D, 0xF9, 0x2D, 0xF0, 0x02, 0x15, 0xAE)

What disks require an MSR?

Every GPT disk must contain an MSR. The order of partitions on the disk should be ESP (if any), OEM (if any) and MSR followed by primary data partition(s). It is particularly important that the MSR be created before other primary data partitions.

Who creates the MSR?

The MSR must be created when disk-partitioning information is first written to the drive. If the manufacturer partitions the disk, the manufacturer must create the MSR at the same time. If Windows partitions the disk during setup, Windows creates the MSR.

Why must the MSR be created when the disk is first partitioned?

After the disk is partitioned, there will be no free space left to create an MSR.

How big is the MSR?

When initially created, the size of the MSR depends on the size of the disk drive: •On drives less than 16GB in size, the MSR is 32MB. •On drives greater than or equal two 16GB, the MSR is 128 MB.

As the MSR is divided into other partitions, it becomes smaller.

BitLocker uses the System (or System Reserved) partition which is different. Further information.

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  • Yeah I read that...This bit is especially interesting "Every GPT disk must contain an MSR." . But it doesn't say if it doesn't contain MSR.It works well without MSR as it did before I accidentally deleted it. – Andrew Jul 17 '15 at 21:54
  • @Andrew Elsewhere it's only 'recommended'. I guess you will be OK unless you do something that requires the reserved space like converting to dynamic disk. – David Marshall Jul 17 '15 at 22:55
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MSR is not needed, removed mine right after Windows thought it had to create that crap on my secondary GPT disk. Works fine ever since (5 years so far) and I even have encrypted the disks via DiskCryptor without any issues.

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Just to add :

  1. Hard disk(s) may develop some bad sectors in the future. Many software programs will be unable to repair/remap it without MSR partition. Thereby making it difficult to make the disk reusable and retrieve the data back.

  2. The name MSR describes Microsoft Reserved Partition in GPT. Don't confuse it with the System Reserved Partition ( MBR Partition scheme).

  3. If you keep MSR, it is very less to loose over to it. It is only 128 MB for Win 7/8 ( On drives less than 16GB in size, the MSR is 32MB ) & 16 MB for win 10!

  4. One may lose it accidentally because it is not shown in windows' in-built Disk Management, but all good 3rd party Partitioning & Imaging programs show it in a graphical view. ( It is also listed in Diskpart's "List Partition" command from the command prompt i.e. Diskpart, List disk, Select disk, List partition & Exit)

  5. DiskGenius makes it very easy to deal with the MSR and EFI partitions. It has an option to create them on the disk directly. It analyzes the drive & proposes the right size for them automatically. If you need to run it from a WinRE, you may check here Or here!

  6. I don't know if recreation will be all that required, but try to put it on your disk exactly after EFI System Partition to maintain the order. That's easily possible with good 3rd party partition tools such as MiniTool Partition Wizard 10.2.2 OR You can use Macrium Reflect Free to image disk partitions individually, initiate the disk again, making all the required partitions & then restoring images individually to those partitions.

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  • Bad sector remapping is primarily done by the disk's internal controller, not by the OS, and it uses hidden spare (overprovisioned) space – it doesn't use any visible partition, as that would mean locking the user into a specific partitioning scheme. And if the disk develops so many sectors that it runs out of the "spare" reallocation space and begins reporting write failures to the OS, then it is already in such a bad condition that reusing it any further is a bad idea. – user1686 Nov 5 '19 at 16:40
  • "The software components that used hidden sectors in MBR partition scheme use MSR to work in GPT". Does it make any further changes ? – Vineet Garg Nov 5 '19 at 17:13
  • This usually refers to the spare sectors in between MBR and the 1st partition, or between the last partition and the end of the disk. (They're not hidden technically – the post-MBR gap is just unused by most partitioning schemes.) For example GRUB would install itself into the post-MBR gap, but on GPT it uses a dedicated partition type. Windows LDM would stash its metadata at the end of a disk, too. – user1686 Nov 5 '19 at 17:31
  • @grawity & all , I don't understand those things. I just followed the two links. – Vineet Garg Nov 7 '19 at 4:49

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