Resizing volumes

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At times you may need to resize a volume. LVM is great for large storage partitions, but if you just need to enlarge a regular EBS volume, this procedure should work. A common example is to expand the size of a root volume to increase storage for applications.

Root Volumes

In the example below, we will assume we are working with an instance's root (OS) volume; if this is not the case, you may skip all steps after resizing the volume (i.e. those steps pertaining to making an image).

The succinct summary of what we will do is: snapshot, save as X GB volume, mount volume and resize partition, created snapshot from X GB volume, registered snapshot as image, boot a new instance of the new image.

BEFORE TAKING SNAPSHOT one must delete the cached MAC address - otherwise one can't ssh to a new VM booted from the snapshot:

rm /etc/udev/rules.d/70-persistent-net.rules

To expand the root partition (assuming the volume is attached to /dev/vdc):

sudo fdisk /dev/vdc 
# [interactive commands to delete root partition (!) and re-create it larger: 
# p, d, p, n, p, 1, defaults... p, w]
sudo sudo e2fsck -f /dev/vdc1
sudo resize2fs /dev/vdc1


Here is a transcript of output from an example procedure:

brandon@euca-128-84-11-149:~$ sudo fdisk /dev/vdc

Welcome to fdisk (util-linux 2.25.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/vdc: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x61e75f2d

Device     Boot Start      End  Sectors Size Id Type
/dev/vdc1  *     2048 20971519 20969472  10G 83 Linux


Command (m for help): d
Selected partition 1
Partition 1 has been deleted.

Command (m for help): p
Disk /dev/vdc: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x61e75f2d



Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 11
Value out of range.
Partition number (1-4, default 1): 1
First sector (2048-62914559, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-62914559, default 62914559):

Created a new partition 1 of type 'Linux' and of size 30 GiB.


Command (m for help): p
Disk /dev/vdc: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x61e75f2d

Device     Boot Start      End  Sectors Size Id Type
/dev/vdc1        2048 62914559 62912512  30G 83 Linux


Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.





brandon@euca-128-84-11-149:~$ sudo resize2fs /dev/vdc1
resize2fs 1.42.12 (29-Aug-2014)
Please run 'e2fsck -f /dev/vdc1' first.

brandon@euca-128-84-11-149:~$ sudo e2fsck -f /dev/vdc1
e2fsck 1.42.12 (29-Aug-2014)
/dev/vdc1: recovering journal
Clearing orphaned inode 475259 (uid=108, gid=116, mode=0100664, size=2379)
Clearing orphaned inode 475232 (uid=108, gid=116, mode=0100664, size=2379)
Clearing orphaned inode 475249 (uid=108, gid=116, mode=0100664, size=2379)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong (578868, counted=578802).
Fix<y>? yes
Free inodes count wrong (344343, counted=344342).
Fix<y>? yes

/dev/vdc1: ***** FILE SYSTEM WAS MODIFIED *****
/dev/vdc1: 311018/655360 files (6.2% non-contiguous), 2042382/2621184 blocks

Scratch disk example

Similarly, you can create a larger scratch disk in the 200 GB of ephemeral space (usually attached to /dev/vdb):

fdisk /dev/vdb [interactive commands: n, p, 1, defaults... p, w]
mke2fs -j /dev/vdb1
e2fsck -f /dev/vdb1
mkdir /scratch
mount -t ext3 /dev/vdb1 /scratch


Logical Volume Manager (LVM)

Users can create partitions larger than 15TB volume limit by employing a logical volume manager within their Linux instance. See this LVM tutorial for an example procedure and useful LVM command; here is a condensed summary of using this tutorial to create an LVM volume and requisite LVM entities to be used as a /home partition for users' home directories which may be increased in size in the future:

fdisk /dev/vdb # Verify this volume looks right (e.g. right size)
apt-get install lvm2 # If not already installed
pvcreate /dev/vdb
pvdisplay # check it shows up
vgcreate myproject_myvolgrp /dev/vdb
lvcreate -L 1090000 -n vol01 myproject_myvolgrp
lvdisplay  # check it shows up
vgdisplay # check free space in volume group, for instance
mkfs.ext4 -m 0 /dev/myproject_myvolgrp/vol01
emacs /etc/fstab # map /dev/myproject_myvolgrp/vol01 to /home

Should you need to detach volumes associated with your LVM group, for instance, to migrate them to a different instance, you can use the procedure illustrated below. This is just attaching all requisite volumes, running 'pvscan', and finally 'lvscan':

root@ubuntu:/# pvscan
  PV /dev/vdb   VG myproject_myvolgrp   lvm2 [1.07 TiB / 35.55 GiB free]
  Total: 1 [1.07 TiB] / in use: 1 [1.07 TiB] / in no VG: 0 [0   ]
root@ubuntu:/# lvscan
  ACTIVE            '/dev/myproject_myvolgrp/vol01' [1.04 TiB] inherit

If all looks well, then you should be able to mount the volume at this point.