[CentOS] Upgrading system from non-RAID to RAID1

Wed Jan 11 14:42:37 UTC 2023
Simon Matter <simon.matter at invoca.ch>

> On 1/11/23 02:09, Simon Matter wrote:
>>> I plan to upgrade an existing C7 computer which currently has one 256
>>> GB
>>> SSD to use mdadmin software RAID1 after adding two 4 TB M2. SSDs, the
>>> rest
>>> of the system remaining the same. The system also has one additional
>>> internal and one external harddisk but these should not be touched. The
>>> system will continue to run C7.
> .... trimming
>>> - I do not see any benefit to breaking up the LVM2/LUKS partition
>>> containing /root, /swap and /home into more than one RAID1 partition or
>>> am
>>> I wrong? If the SSD fails, the entire SSD would fail and break the
>>> system,
>>> hence I might as well keep it as one single RAID1 partition, or?
>> 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.
> Ah, now I begin to get it.  Separate partitions RAIDed.

Yes, exactly, sorry for not being clear enough. The structure of disk 0
looks like this:

$ lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT /dev/nvme0n1
NAME            FSTYPE              SIZE MOUNTPOINT
nvme0n1                           745.2G
├─nvme0n1p1     vfat                200M /boot/efi
├─nvme0n1p2     linux_raid_member     1G
│ └─md0         xfs                1023M /boot
├─nvme0n1p3     linux_raid_member   186G
│ └─md1         LVM2_member       185.9G
│   ├─main-root xfs                  30G /
│   ├─main-swap swap                 16G [SWAP]
│   ├─main-tmp  xfs                  10G /tmp
│   ├─main-var  xfs                 200G /var
│   └─main-imap xfs                 1.2T /var/spool/imap
├─nvme0n1p4     linux_raid_member   186G
│ └─md2         LVM2_member       185.9G
│   └─main-imap xfs                 1.2T /var/spool/imap
├─nvme0n1p5     linux_raid_member   186G
│ └─md3         LVM2_member       185.9G
│   └─main-imap xfs                 1.2T /var/spool/imap
├─nvme0n1p6     linux_raid_member   186G
│ └─md4         LVM2_member       185.9G
│   ├─main-var  xfs                 200G /var
│   └─main-imap xfs                 1.2T /var/spool/imap
└─nvme0n1p7                        15.8M