Failed HDD on Windows Server 2019 and wont boot

Hi, already resolved this, but I'll detail how below using OVH Windows rescue. Please note how you're existing, working drive is partitioned. If it comes up as "Foreign Disk", you'll need to "Import" them before you can see them. Be VERY careful, one wrong command, and you could wipe all your data on the disk that remains! Get backups before-hand just in-case.

This shows you how to MANUALLY re-create the EFI partition. You can also do this on the EFI partition if it's become corrupt, but just remember your Windows partition will be on this drive already! Careful.

1). The new disc will be uninitialised, so initialise as GPT.
2). Use Disk Manager to create 350MB, or however big the EFI partition is on your other drive. This will be at the front of the new drive.
3). Use Disk Man to partition the rest, no need to format for now.
4). Remove 350MB partition.
5). Run "diskpart" and select the new disk, (make sure this is correct).
6). Then run: "create partition EFI". This will create the EFI partition on the new drive.
7). Then use diskpart to assign a drive letter as below:
(You need to select the correct Volume. List them in diskpart with: list vol)
sel vol x (replace the "x" with the correct number from "list vol" as above).
assign letter=v
exit
8). Once done, run the below on the new partition with the drive letter to format as FAT32:
format v: /fs:fat32

(You need to point the server's windows install, NOT the rescue partition! In my case, it was E:\Windows)
bcdboot E:\Windows /s v: /f UEFI

Now the important part! If you're using a Software Raid 1, you will need to rebuild the software array AND wait for it to complete. Can take hours on say 4TB HDD drive. As this new drive will be booting, it needs the data to sync back. If you have an SSD for boot and OS, it will be quick, and you can sort the larger HDD drivers later once you're back into your main Windows OS.

Once done, reboot using Server Boot HD and hopefully it's back up. Not the best guide, but it got me back up and running.

Hello @tazau

> are you saying it has been installed to the second efs partiton and will auto detect this

Yes, when the OS was installed, all ESPs were synced by our system. Usually, the ESPs only contain a stub GRUB config file that rarely needs to be updated.
When a disk is changed, the rEFInd bootloader will detect the EFI applications on the secondary ESP and use them.

> would we have to update FSTAB to the other drive in the event the first one failed?
If you're using our default installation, we mount the ESP by its label and all ESPs have the same so you wouldn't need to change it.
However, I would still recommend creating a new ESP on the replaced disk, setting its label with `fatlabel` and syncing data to it.

Here's a script I provided that relies on labels to sync all ESPs: https://community.ovh.com/t/Partition-EFI-sur-raid-apr%C3%A8s-changement-de-disque/60512/9