playground/aws/how-to-make-multiple-parttions-on-root-device.md

Date: Aug 25, 2021

The volume created of Amazon Linux 2 AMI(HVM), SSD Volume Type - ami-0f511ead81ccde020(64-bit x86) contains two partitions in the GPT partition table. The first partition is the Bios Boot Partition that stores the second stage of the boot loader such as GNU grub. The second partition is the actual root partition.

```
 parted /dev/xvda
GNU Parted 3.1
Using /dev/xvda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvda: 16.1GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name                 Flags
128     1049kB  2097kB  1049kB               BIOS Boot Partition  bios_grub
 1      2097kB  16.1GB  16.1GB  xfs          Linux

(parted)
```

Do the followings in the AWS console or with the AWS cli command.

- Create two EC2 instances with the same configuration. Namely IX and IY.
- Let's call the default volumes attached VX and VY respectively.
- Stop both instances.
- Create 1 extra volume off the instances. Namely, VZ,  (10GB in this sample)
- Detach VY from IY and attach it to IX as /dev/sdf
- Attach VZ to IX as /dev/sdg
- Start IX and connect to it.

Do the followings as root inside IX.
- Check the available block devices with lsblk.

```
# lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0  15G  0 disk 
└─xvda1 202:1    0  15G  0 part /
xvdf    202:80   0   8G  0 disk 
└─xvdf1 202:81   0   8G  0 part 
xvdg    202:96   0  10G  0 disk 
```

- Parition VZ (/dev/xvdg) according to your own needs. Ensure to create the BIOS Boot Partition. 
```
# parted /dev/xvdg
GNU Parted 3.1
Using /dev/xvdg
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Error: /dev/xvdg: unrecognised disk label
Model: Xen Virtual Block Device (xvd)                                     
Disk /dev/xvdg: 10.7GB
Sector size (logical/physical): 512B/512B
Partition Table: unknown
Disk Flags: 
(parted) mklabel gpt                                                      
(parted) mkpart 'BIOS Boot Partition' 1MB 2MB
(parted) set 1 bios_grub on                                               
(parted) mkpart root xfs 2MB 50%                                          
(parted) mkpart data xfs 50% 95%
(parted) mkpart swap linux-swap 95% 100%                                  
(parted) p                                                                
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvdg: 10.7GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name                 Flags
 1      1049kB  2097kB  1049kB               BIOS Boot Partition  bios_grub
 2      2097kB  5369MB  5367MB               root
 3      5369MB  10.2GB  4832MB               data
 4      10.2GB  10.7GB  536MB                swap

(parted) q                                                                
Information: You may need to update /etc/fstab.
```

- Check recognized block devices again.
```
# lsblk                                   
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   15G  0 disk 
└─xvda1 202:1    0   15G  0 part /
xvdf    202:80   0    8G  0 disk 
└─xvdf1 202:81   0    8G  0 part 
xvdg    202:96   0   10G  0 disk 
├─xvdg1 202:97   0    1M  0 part 
├─xvdg2 202:98   0    5G  0 part 
├─xvdg3 202:99   0  4.5G  0 part 
└─xvdg4 202:100  0  511M  0 part 
```

- Create file systems on xvdf1 and xvdg2 in the xfs format.

```
# mkfs -t xfs -f /dev/xvdg2
meta-data=/dev/xvdg2             isize=512    agcount=4, agsize=327552 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=0
data     =                       bsize=4096   blocks=1310208, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
# mkfs -t xfs -f /dev/xvdg3
meta-data=/dev/xvdg3             isize=512    agcount=4, agsize=294912 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=0
data     =                       bsize=4096   blocks=1179648, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
```

- Copy everything from xvdf1 to xvdg2.
```
# mount /dev/xvdf1 /mnt/vy
# mount /dev/xvdg2 /mnt/vz
# rsync -av /mnt/vy/ /mnt/vz/
# umount /mnt/vy
```

- Update /mnt/vz/etc/fstab to match the UUID of xvdg2.

```
# blkid | grep xvdg2
/dev/xvdg2: UUID="e47315e4-ff01-49b0-81f7-bac53f08a88b" TYPE="xfs" PARTLABEL="root" PARTUUID="de12b03c-53ff-4f53-b990-1d823f42a7aa"
[root@ip-172-31-18-121 ~]# cat /mnt/vz/etc/fstab
#
UUID=04b92f2f-4366-4687-868b-7c403cc59901     /           xfs    defaults,noatime  1   1
# sed -i 's|04b92f2f-4366-4687-868b-7c403cc59901|e47315e4-ff01-49b0-81f7-bac53f08a88b|g' /mnt/vz/etc/fstab
[root@ip-172-31-18-121 ~]# cat /mnt/vz/etc/fstab
#
UUID=e47315e4-ff01-49b0-81f7-bac53f08a88b     /           xfs    defaults,noatime  1   1
```

- Update /mnt/vz/boot/grub2/grub.cfg
```
# mv /mnt/vz/boot/grub2/grub.cfg /mnt/vz/boot/grub2/grub.cfg.org
# sed  's|04b92f2f-4366-4687-868b-7c403cc59901|e47315e4-ff01-49b0-81f7-bac53f08a88b|g'  /mnt/vz/boot/grub2/grub.cfg.org > /mnt/vz/boot/grub2/grub.cfg
```
While ```grub2-mkconfig -o /mnt/vz/boot/grub2/grub.cfg``` is a proper command, it inserts the menu entries using the current boot partition(VX). The sample above substituted the UUID of xvdg2 for the auto-produced UUIDs. If you want to skip updating fstab and grub.cfg, you may consider setting the UUID of xvdg2 to match that of xvdf1.

- Install the grub boot loader on /dev/xvdg and unmount /dev/xvdg2
```
# grub2-install --target=i386-pc --directory=/mnt/vz/usr/lib/grub/i386-pc --recheck --boot-directory=/mnt/vz/boot /dev/xvdg
Installing for i386-pc platform.
Installation finished. No error reported.
# umount /dev/xvdg2
```

Do the followings in the AWS console or with the AWS cli command.
- Stop the instance IX.
- Detach the volume VZ from IX.
- Attach VZ to IY as /dev/xvda.
- Start IY.

IY has the boot device volume with 2 normal partitions, 1 swap partition, and 1 BIOS Boot partition. The second normal partition labeled 'data' is left free for your own disposal.

```
# parted /dev/xvda
GNU Parted 3.1
Using /dev/xvda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p                                                                
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvda: 10.7GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name                 Flags
 1      1049kB  2097kB  1049kB               BIOS Boot Partition  bios_grub
 2      2097kB  5369MB  5367MB  xfs          root
 3      5369MB  10.2GB  4832MB  xfs          data
 4      10.2GB  10.7GB  536MB                swap

(parted)
# df
Filesystem     1K-blocks    Used Available Use% Mounted on
devtmpfs          492676       0    492676   0% /dev
tmpfs             503444       0    503444   0% /dev/shm
tmpfs             503444     500    502944   1% /run
tmpfs             503444       0    503444   0% /sys/fs/cgroup
/dev/xvda2       5230592 1565416   3665176  30% /
tmpfs             100692       0    100692   0% /run/user/1000
tmpfs             100692       0    100692   0% /run/user/0
# mount /dev/xvda3 /mnt
# df
Filesystem     1K-blocks    Used Available Use% Mounted on
devtmpfs          492676       0    492676   0% /dev
tmpfs             503444       0    503444   0% /dev/shm
tmpfs             503444     500    502944   1% /run
tmpfs             503444       0    503444   0% /sys/fs/cgroup
/dev/xvda2       5230592 1565416   3665176  30% /
tmpfs             100692       0    100692   0% /run/user/1000
tmpfs             100692       0    100692   0% /run/user/0
/dev/xvda3       4183040   37200   4145840   1% /mnt
```
You may enable the swap in the swap partition. If you don't need it, you can change the partition type and format it to a normal file system. You are free to use /dev/xvda3 the way you like.

## Summary
- Copy everything from the standard volume to one of the partitions of the new volume
- Update the boot loader and fstab

## TODO
automate the entire process with the AWS CLI or other tools.