[GLLUG] Link two RAIDs in one LVM?

[Dr. Axel Stammler]

On Sun 2020-05-10 08.53.16, James Courtier-Dutton wrote:

>So, there is a solution that uses tiled RAID. LVM has a "mirror" option.
>https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/4/html/cluster_logical_volume_manager/mirrored_volumes
>If you used that, you would not need a RAID layer at all.
>You would create all the disks as a LVM volume group, and then create
>LVM partitions using the LVM mirror option.
>An LVM mirror divides the device being copied into regions that are
>typically 512KB in size, so a big improvement over the 500GB chunks
>suggestion above.
>This would also give flexibility, you could choose some of your data
>to be "mirror" and some not.
>LVM "mirror" also lets you migrate data while it is still mounted.
>You have the original LVM volume, mirror it onto a new disk, remove
>the original copy.
>
>So, I think moving to an "LVM mirror" solution is your best bet for
>future extensibility.

After reviewing all options, this indeed seems to be the best one in my case. As I am doing for the first time — are these the correct steps?

* additional sources I looked at:
- https://wiki.debian.org/LVM
- https://www.debian.org/doc/manuals/debian-handbook/advanced-administration.en.html#sect.raid-and-lvm

[new hard disk drives, still blank: sdc, sde; old hard disk drives as RAID-1 system md127p1]

pvcreate /dev/sdc
pvcreate /dev/sde

vgcreate vg_blobs /dev/sdc /dev/sde

lvcreate -n lv_blobs -m1 vg_blobs # How do I make the new volume use all available space? Will mirroring choose the physical volumes automatically? Where does the log go? = Do I need a partition on a separate disk for it? How large should it be and how do I incorporate it?

mkfs.ext4 /dev/vg_blobs/lv_blobs

rsync … # old RAID-1 system ↔ new mirrored volume group

# ? remove sda + sdb from RAID-1 md127p1
# ? eliminate RAID-1 md127p1

pvcreate /dev/sda
pvcreate /dev/sdb

vgextend vg_blobs *** # or vgcreate vg_blobs2 ?

lvextend / lvresize # ?

# grow filesystem
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