Partitions A Thing Of The Past 3
Here, I'll start with a standard Linux disk setup and will show the steps required to migrate to a partitionless one consisting of three disks -
one for /boot, one for swap and one for /. Extending this example to add other drives for /var, /tmp and /home is left to the reader.
First, here's the partition scheme of my VM running Ubuntu 10.04, in 512-byte sectors. Primary partition #1 is for the / file system, and also
has the MBR with grub installed:
root@ubuntu:~# parted -s /dev/sda 'u s p'
Model: VMware Virtual disk (scsi)
Disk /dev/sda: 33554432s
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 2048s 29190143s 29188096s primary ext4 boot
2 29190144s 33552383s 4362240s primary linux-swap(v1)
#Step 1: Add disk for boot data and move existing boot partition to new disk#
Add 512MB SCSI disk 0:1 in VMWare vSphere client:
Use rescan-scsi-bus.sh to scan drives. rescan-scsi-bus.sh requires that the scsitools package be installed and can be downloaded from
http://rescan-scsi-bus.sh (neat huh?)
root@ubuntu:~# ./rescan-scsi-bus.sh
Host adapter 0 (ata_piix) found.
Host adapter 1 (ata_piix) found.
Host adapter 2 (mptspi) found.
Scanning SCSI subsystem for new devices
Scanning host 0 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs
Scanning host 1 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs
Scanning for device 1 0 0 0 ...
OLD: Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: NECVMWar Model: VMware IDE CDR10 Rev: 1.00
Type: CD-ROM ANSI SCSI revision: 05
Scanning host 2 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs
Scanning for device 2 0 0 0 ...
OLD: Host: scsi2 Channel: 00 Id: 00 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
Scanning for device 2 0 1 0 ...
NEW: Host: scsi2 Channel: 00 Id: 01 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
1 new device(s) found.
0 device(s) removed.
The new drive is now /dev/sdb. The following commands will set it up:
root@ubuntu:~# parted -s /dev/sdb 'mklabel msdos' # Creates MBR partition table
root@ubuntu:~# parted -s /dev/sdb 'u s mkpart primary 2048 1048575' # Creates single primary partition
root@ubuntu:~# parted -s /dev/sdb 'set 1 boot on' # Marks drive bootable
This command will turn off the boot flag on the first drive (/dev/sda):
root@ubuntu:~# parted -s /dev/sda 'set 1 boot off'
Create an ext2 file system on the new drive's first partition (/dev/sdb1):
root@ubuntu:~# mkfs -t ext2 -L boot /dev/sdb1
mke2fs 1.41.11 (14-Mar-2010)
Filesystem label=boot
OS type: Linux
...
...
Add to /etc/fstab:
root@ubuntu:~# cp /etc/fstab /etc/fstab.orig
root@ubuntu:~# blkid -o value -s UUID /dev/sdb1
bb659f0c-b85d-467f-a61f-f0d3657d446d
New fstab (added /boot line with the above UUID):
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
UUID=bb659f0c-b85d-467f-a61f-f0d3657d446d /boot ext2 errors=remount-ro,nodev 0 0
UUID=4a63db92-1b92-4b5c-bf29-31a2f8f7a875 / ext4 errors=remount-ro 0 1
UUID=e3d681e6-54d5-4851-b551-e3631394e2f8 none swap sw 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0
Mount and copy the existing /boot directory to the new drive:
root@ubuntu:~# mount /dev/sdb1 /mnt
root@ubuntu:~# tar -C /boot -cpf - . | tar -C /mnt -xpvf -
Unmount and remount as /boot:
root@ubuntu:~# umount /mnt; mount /dev/sdb1 /boot
Install and update grub. Note: it is very important to run update-grub as it will update /boot/grub/grub.cfg with correct device UUIDs
root@ubuntu:~# grub-install /dev/sdb
Installation finished. No error reported.
root@ubuntu:~# update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.32-45-server
Found initrd image: /boot/initrd.img-2.6.32-45-server
Found linux image: /boot/vmlinuz-2.6.32-24-server
Found initrd image: /boot/initrd.img-2.6.32-24-server
Found memtest86+ image: /memtest86+.bin
done
Unmount and move existing /boot out of the way:
root@ubuntu:~# umount /boot
root@ubuntu:~# mv /boot /boot.orig
root@ubuntu:~# mkdir /boot
Shutdown VM. In vSphere client, swap disk settings so that new boot disk is SCSI 0:0 and prior disk is 0:1
Start VM and confirm:
root@ubuntu:~# mount | fgrep sd
/dev/sdb1 on / type ext4 (rw,errors=remount-ro)
/dev/sda1 on /boot type ext2 (rw,nodev,errors=remount-ro)
root@ubuntu:~# parted -l
Model: VMware Virtual disk (scsi)
Disk /dev/sda: 537MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 537MB 536MB primary ext2 boot
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 17.2GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 14.9GB 14.9GB primary ext4
2 14.9GB 17.2GB 2233MB primary linux-swap(v1)
Add 2GB SCSI disk 0:2 in vSphere client as above and use rescan-scsi-bus.sh to scan drives. The new drive is now /dev/sdc.
Set up the entire disk as swap space:
root@ubuntu:~# mkswap -f /dev/sdc
Setting up swapspace version 1, size = 2097148 KiB
no label, UUID=d761cf3e-35e6-450c-aa17-4f96b91b79b6
Add to /etc/fstab:
root@ubuntu:~# cp /etc/fstab /etc/fstab.orig1
root@ubuntu:~# vi /etc/fstab
New fstab (modified the UUID in the 'swap' line):
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
UUID=bb659f0c-b85d-467f-a61f-f0d3657d446d /boot ext2 errors=remount-ro,nodev 0 0
UUID=4a63db92-1b92-4b5c-bf29-31a2f8f7a875 / ext4 errors=remount-ro 0 1
UUID=d761cf3e-35e6-450c-aa17-4f96b91b79b6 none swap sw 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0
Enable new swap, disable old:
root@ubuntu:~# swapon -s
Filename Type Size Used Priority
/dev/sdb2 partition 2181112 0 -1
root@ubuntu:~# swapon -a
root@ubuntu:~# swapon -s
Filename Type Size Used Priority
/dev/sdb2 partition 2181112 0 -1
/dev/sdc partition 2097144 0 -2
root@ubuntu:~# swapoff /dev/sdb2
root@ubuntu:~# swapon -s
Filename Type Size Used Priority
/dev/sdc partition 2097144 0 -1
Shutdown VM and move SCSI disk 0:2 to 0:1 and old 0:1 to 0:2. We want swap to be /dev/sdb.
Power on VM, confirm:
root@ubuntu:~# parted -l
Model: VMware Virtual disk (scsi)
Disk /dev/sda: 537MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 537MB 536MB primary ext2 boot
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 2147MB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Number Start End Size File system Flags
1 0.00B 2147MB 2147MB linux-swap(v1)
Model: VMware Virtual disk (scsi)
Disk /dev/sdc: 17.2GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 14.9GB 14.9GB primary ext4
2 14.9GB 17.2GB 2233MB primary linux-swap(v1)
root@ubuntu:~# swapon -s
Filename Type Size Used Priority
/dev/sdb partition 2097144 0 -1
Add 16GB SCSI disk 0:3 in vsphere client and use rescan-scsi-bus.sh to scan drives. Drive is now /dev/sdd.
Create file system. Note: it'll warn you about using the entire device, which is what we want:
root@ubuntu:~# mkfs -t ext4 -L root /dev/sdd
mke2fs 1.41.11 (14-Mar-2010)
/dev/sdd is entire device, not just one partition!
Proceed anyway? (y,n) y
Filesystem label=root
OS type: Linux
...
...
Shut down this VM. Create a VM that will run the Linux System Rescue CD and edit VM settings to attach the
original disk (QA1LRBUBU12.vmdk in my case) as SCSI 0:0 (/dev/sda) and the newest disk (QA1LRBUBU_3.vmdk) as SCSI 0:1 (/dev/sdb):
Power on the System Rescue VM and confirm disks:
Here you will make mount points and copy files from old root to new root:
root@ubuntu:~# mkdir /mnt/sda1
root@ubuntu:~# mkdir /mnt/sdb
root@ubuntu:~# mount /dev/sda1 /mnt/sda1
root@ubuntu:~# mount /dev/sdb /mnt/sdb
root@ubuntu:~# tar -C /mnt/sda1 -cpf - . | tar -C /mnt/sdb -xpf -
Edit /mnt/sdb/etc/fstab to make the /dev/sdb disk the root disk. The >> /mnt/sdb/etc/fstab will make your life easier as it will append
the new UUID to the end of the fstab and then you just need to move it around with your text editor:
root@ubuntu:~# cp /mnt/sdb/etc/fstab /mnt/sdb/etc/fstab.orig2
root@ubuntu:~# blkid -o value -s UUID /dev/sdb >> /mnt/sdb/etc/fstab
root@ubuntu:~# vi /mnt/sdb/etc/fstab
New fstab (the UUID in the / line changed):
Power off the System Rescue VM and detach the disks. Attach the new boot disk (QA1LRBUBU12_1.vmdk) as 0:0 (/dev/sda) and the new root file
system disk (QA1LRBUBU12_3.vmdk) as 0:1 (/dev/sdb). Power on the System Rescue VM and ensure you have the right disks attached:
We need to update the UUID of the root disk in grub's configuration. There's no easy way to do this other than to replace UUID values in the grub configuration file:
root@ubuntu:~# mkdir /mnt/sda1
root@ubuntu:~# mkdir /mnt/sdb
root@ubuntu:~# mount /dev/sda1 /mnt/sda1 # this is the new boot disk
root@ubuntu:~# mount /dev/sdb /mnt/sdb # this is the new root file system disk
The /mnt/sda1/grub/grub.cfg file will contain the UUID of the old root disk, and we need to replace it with the new UUID:
root@ubuntu:~# fgrep -i root=UUID /mnt/sda1/grub/grub.cfg > uuid.sh
root@ubuntu:~# blkid -o value -s UUID /dev/sdb >> uuid.sh
root@ubuntu:~# vi uuid.sh
Edit uuid.sh to run this command:
sed -i.bak 's/OLD-UUID/NEW-UUID/g' /mnt/sda1/grub/grub.cfg
Then, run the command and confirm
Power off the System Rescue VM and detach all disks. In original VM detach the original disk which is SCSI 0:2 and move SCSI 0:3 to 0:2
Power on original VM and confirm. We should also re-run "update-grub" to ensure that grub.cfg is the auto-generated version. Then ... DONE!
root@ubuntu:~# parted -l
Model: VMware Virtual disk (scsi)
Disk /dev/sda: 537MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 537MB 536MB primary ext2 boot
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 2147MB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Number Start End Size File system Flags
1 0.00B 2147MB 2147MB linux-swap(v1)
Model: VMware Virtual disk (scsi)
Disk /dev/sdc: 17.2GB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Number Start End Size File system Flags
1 0.00B 17.2GB 17.2GB ext4
root@ubuntu:~# swapon -s
Filename Type Size Used Priority
/dev/sdb partition 2097144 0 -1
root@ubuntu:~# update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.32-45-server
Found initrd image: /boot/initrd.img-2.6.32-45-server
Found linux image: /boot/vmlinuz-2.6.32-24-server
Found initrd image: /boot/initrd.img-2.6.32-24-server
Found memtest86+ image: /memtest86+.bin
done
Also, note the difference in physical size vs. provisioned size of the disks:
In the next part of this series, I'll look into the LVM feature set and how using partitionless disks in a virtualized environment eliminates the need for LVM entirely.