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I am trying to install debain 9 and have a question about partitioning. I install Debian via uefi and use software RAID which distributes my root filesystem and swap partitions to my hard disks. However, I don't know if I have to create an efi partition or a biosgrub partition. As far as I know, the efi partition contains the biosgrub data. However, the Debian website says that it is not yet possible to distribute an efi partition with RAID on several disks. So do I have to create an efi partition on all 3 disks? And what if a hard disk fails, is one of the other 2 efi partitions used? And do I have to activate "boot flag" on the efi partitions?

  • AFAIK it's not solved yet indeed (I've implemented UEFI support in ALT Linux and we've got a corresponding bugreport as well); the manual scheme will require manual sync when your /boot/efi contents change (that's at least when grub gets updated); maybe consider a separate SATA DOM or even USB Flash for your /boot and RAIDing down everything else starting with root partition. – Michael Shigorin Jan 21 '18 at 14:32
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Do I have to create an efi partition on all 3 disks?

No, you can simply create the EFI partition on one of the disks.

However, this may impact how well RAID can utilize you hard disks because in some RAID configurations storage is allocated in equal amounts on each disk. In such a case, the amount of space utilized by the EFI partition will not be utilized in the other disks.

An alternative is to add a disk only for EFI, or for EFI and non-RAID partitions.

If a hard disk fails, is one of the other 2 EFI partitions used?

I don't know.

And do I have to activate "boot flag" on the EFI partitions?

No, the EFI partition is marked as such by the partition type ef00, not by the boot flag.

  • Erm, if partitioning is identical and it's Linux MD RAID I don't see any potential for performance impact. ...PS: ah, you meant the different partitioning indeed; well doing it symmetrical just makes sense anyways. – Michael Shigorin Jan 21 '18 at 14:29
  • I don't see anything that would stop three distinct copies of grub sitting on three separate ESPs from working but that's not supported by distro kernel/grub update scripts anywhere AFAIK, maintaining those (with e.g. "debian1/debian2/debian3" NVRAM records) will take some manual labour. – Michael Shigorin Jan 21 '18 at 14:36
  • Correct. I suspect having an ESP on each drive would work in the sense the system would boot, but I don't know of a distro which supports keeping multiple boot partitions up-to-date. One hack is to write a script which treats one of the ESPs as a master and uses rsync to keep the other ESP filesystems up to date. A systemd timer can be used to run the script, or it can be executed manually after each OS update. As for the NVRAM records, maybe something can be done with efibootmgr. – Emmanuel Rosa Jan 21 '18 at 15:09

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