Disks

Harddisks

1. Firmware
2. ATA, SCSI Driver
3. Physical Block Devices
4. MBR, UEFI GPT Partitions
5. LVM2 Physcical Volume (disk or partition)
7. Volume Group, spanning physical volumes
8. Logical Volumes
9. Device Mapper
10.Filesystem

Harddisk

ls -al /dev/disk/by*
blkid

/dev/xvda2: UUID="2ab116ed-fdae-4ee6-aafd-f2febf9a4a96" TYPE="ext4" PARTUUID="3278fa68-67cf-476f-88e1-fa858160c1c5"
/dev/xvda3: UUID="9O6sva-rWF6-DO3I-GKIz-iuMg-qrQo-y13KV4" TYPE="LVM2_member" PARTUUID="478fca97-0ca6-4597-aaa6-e709947d1868"
/dev/xvdb: UUID="0d331770-95d3-4d15-839a-cce7ddcb6741" TYPE="ext4"
/dev/mapper/ubuntu--vg-ubuntu--lv: UUID="597d1543-fe70-4f53-9d82-7fb0c2249ac7" TYPE="ext4"

Disks may have partitions or raw. Partion tables can be the newer GPT UEFI style, or the old MBR masterbootrecord BIOS style, limited to 4 partitions and one can be extended to house more partions, one can be 'active' which windows can boot from.

https://en.wikipedia.org/wiki/GNU_GRUB#/media/File:GNU_GRUB_on_GPT_partitioned_hard_disk_drives.svg

Boot process, grub in the first 512bytes, menu which partition to find the kernel, the initfs kernel modules and where the rootf is.

GPT

fdisk
cfdisk
cgdisk
sfdisk
sgdisk

S for scriptable, F for BIOS/MBR layout, G for UEFI/GPT layout
sfdisk -l

Temp partition

Format, Journaling

mount

parted partmagic losetup

LVM

https://en.wikipedia.org/wiki/GNU_GRUB#/media/File:GNU_GRUB_on_GPT_partitioned_hard_disk_drives.svg

Physical volume
Volume group
Logical volume

apk add lvm2
insmod lvm
vgchange -ay

pvdisplay
vgdisplay
lvdisplay

vgchange -ay

lvcreate -L 32G -n ubuntest-hvm /dev/vg0
dd if=/dev/vg0/ubuntu-hvm of=/dev/vg0/ubuntest-hvm

lvremove /dev/vg0/truenas-hvm

lvcreate -L 16G -n truenas-hvm /dev/vg0
lvcreate -l 100%FREE -n truenas-pool /dev/vg0

  --- Logical volume ---
 LV Path                /dev/vg0/ubuntest-hvm
 LV Name                ubuntest-hvm
 VG Name                vg0
 LV UUID                OZeTmq-fCJ3-HY87-vLkH-0G2m-bPKo-SCMpwm
 LV Write Access        read/write
 LV Creation host, time nl, 2020-11-08 12:15:41 +0000
 LV Status              available
 # open                 0
 LV Size                32.00 GiB
 Current LE             8192
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:4
  
 --- Logical volume ---
 LV Path                /dev/vg0/data
 LV Name                data
 VG Name                vg0
 LV UUID                3wIcBP-IM69-It1X-2QGs-Bczs-KIvA-wb54hG
 LV Write Access        read/write
 LV Creation host, time nl, 2020-12-30 08:14:01 +0000
 LV Status              available
 # open                 1
 LV Size                89.97 GiB
 Current LE             23033
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:5

apk add device-mapper sfdisk multipath-tools
dmsetup ls
dmsetup info vg0-data
sfdisk -l /dev/mapper/vg0-data
kpartx -av /dev/mapper/vg0-data
mount /dev/mapper/vg0-data1 /data

=== Extend VG/LV ===

pvcreate /dev/sdb
vgextend ubuntu-vg /dev/sdb
lvextend -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv

=== Next level ===

Mounting a nested volume group, which is in a GPT inside a Logical Volume, through the dev mapper using kpartx in multipath-tools

apk add multipath-tools
kpartx -av /dev/mapper/vg0-data
mount -t ext4 /dev/mapper/vg0-data1 /data

sfdisk /dev/vg0/data
dmsetup info vg0-data

vgchange -ay

mount /dev/dm-4 /data/
mount -t ext4 /dev/dm-4 /data/
mount -t vfat /dev/dm-4 /data/
mount -t vfat /dev/dm-4 /data/
mount -v -t vfat /dev/dm-4 /data/
mount -vvv -t vfat /dev/dm-4 /data/
strace mount -t vfat /dev/dm-4 /data/
strace mount -t vfat /dev/dm-4 /data/
mount -vvv -t vfat /dev/dm-4 /data/

sfdisk /dev/vg0/data

file -s /dev/vg0/data
file -s /dev/mapper/vg0-data
file /dev/vg0/data
file /dev/mapper/vg0-data
ls -la /dev/vg0/data
mount /dev/mapper/vg0-data /data