[CentOS] Upgrading system from non-RAID to RAID1

Thu Jan 12 06:56:36 UTC 2023
Simon Matter <simon.matter at invoca.ch>

> On 01/11/2023 01:33 PM, H wrote:
>> On 01/11/2023 02:09 AM, Simon Matter wrote:
>>> What I usually do is this: "cut" the large disk into several pieces of
>>> equal size and create individual RAID1 arrays. Then add them as LVM PVs
>>> to
>>> one large VG. The advantage is that with one error on one disk, you
>>> wont
>>> lose redundancy on the whole RAID mirror but only on a partial segment.
>>> You can even lose another segment with an error on the other disk and
>>> still have redundancy if the error is in another part.
>>> That said, it's a bit more work to setup but has helped me several
>>> times
>>> in the decades ago.
>> But is your strategy of dividing the large disk into individual RAID1
>> arrays also applicable to SSDs? I have heard, perhaps incorrectly, that
>> once a SSD fails, the entire SSD becomes unusable which would suggest
>> that dividing it into multiple RAID1 arrays would not be useful?
> Follow-up question: Is my proposed strategy below correct:
> - Make a copy of all existing directories and files on the current disk
> using clonezilla.
> - Install the new M.2 SSDs.
> - Partitioning the new SSDs for RAID1 using an external tool.
> - Doing a minimal installation of C7 and mdraid.
> - If choosing three RAID partitions, one for /boot, one for /boot/efi and
> the third one for the rest, do I go with the default mdraid version, ie
> 1.2 I believe?

I think at least /boot/efi must be on an mdraid version which has its
metadata at the end of the partition, I'm not sure about /boot.
That said, I think the installer should take care here but I'm not sure it
already does on C7.

> - Copying the backup above with contents of the the existing disks, ie not
> just /root and /home but all other directories and files to the new disks
> from the clonezilla backup. Note that the new disks will be larger.

I can't comment on clonezilla as I've never used it. Tar and rsync are my
friends when doing such things.
I think you may have to take special care for boot related stuff like
things in /boot and boot/efi. The other thing to care is for hardware
related stuff like UUIDs generated in /etc/udev. The whole undertaking is
not trivial.

> - Change the boot sequence in the BIOS and reboot.

That's EFI, yes? I still fell like a greenhorn with EFI :)