[CentOS] RAID1 setup

Mon Jan 9 06:32:02 UTC 2023
Simon Matter <simon.matter at invoca.ch>


> Continuing this thread, and focusing on RAID1.
> I got an HPE Proliant gen10+ that has hardware RAID support.  (can turn
> it off if I want).

What exact model of RAID controller is this? If it's a S100i SR Gen10 then
it's not hardware RAID at all.

> I am planning two groupings of RAID1 (it has 4 bays).
> There is also an internal USB boot port.
> So I am really a newbie in working with RAID.  From this thread it
> sounds like I want /boot and /boot/efi on that USBVV boot device.

I suggest to use the USB device only to bot the installation medium, not
use it for anything used by the OS.

> Will it work to put / on the first RAID group?  What happens if the 1st
> drive fails and it is replaced with a new blank drive.  Will the config
> in /boot figure this out or does the RAID hardware completely mask the 2
> drives and the system runs on the good one while the new one is being
> replicated?

I guess the best thing would be to use Linux Software RAID and create a
small RAID1 (MD0) device for /boot and another one for /boot/efi (MD1),
both in the beginning of disk 0 and 1 (MD2). The remaining space on disk 0
and 1 are created as another MD device. Disk 2 and 3 are also created as
one RAID1 (MD3) device. Formatting can be done like this

MD0 has filesystem for /boot
MD1 has filesystem for /boot/efi
MD2 is used as LVM PV
MD3 is used as LVM PV

All other filesystems like / or /var or /home... will be created on LVM
Logical Volumes to give you full flexibility to manage storage.


> I also don't see how to build that boot USB stick.  I will have the
> install ISO in the boot USB port and the 4 drives set up with hardware
> RAID.  How are things figure out?  I am missing some important piece here.
> Oh, HP does list Redhat support for this unit.
> thanks for all help.
> Bob
> On 1/6/23 11:45, Chris Adams wrote:
>> Once upon a time, Simon Matter <simon.matter at invoca.ch> said:
>>> Are you sure that's still true? I've done it that way in the past but
>>> it
>>> seems at least with EL8 you can put /boot/efi on md raid1 with metadata
>>> format 1.0. That way the EFI firmware will see it as two independent
>>> FAT
>>> filesystems. Only thing you have to be sure is that nothing ever writes
>>> to
>>> these filesystems when Linux is not running, otherwise your /boot/efi
>>> md
>>> raid will become corrupt.
>>> Can someone who has this running confirm that it works?
>> Yes, that's even how RHEL/Fedora set it up currently I believe.  But
>> like you say, it only works as long as there's no other OS on the system
>> and the UEFI firmware itself is never used to change anything on the FS.
>> It's not entirely clear that most UEFI firmwares would handle a drive
>> failure correctly either (since it's outside the scope of UEFI), so IIRC
>> there's been some consideration in Fedora of dropping this support.
>> And... I'm not sure if GRUB2 handles RAID 1 /boot fully correctly, for
>> things where it writes to the FS (grubenv updates for "savedefault" for
>> example).  But, there's other issues with GRUB2's FS handling anyway, so
>> this case is probably far down the list.
>> I think that having RAID 1 for /boot and/or /boot/efi can be helpful
>> (and I've set it up, definitely not saying "don't do that"), but has to
>> be handled with care and possibly (probably?) would need manual
>> intervention to get booting again after a drive failure or replacement.
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