How to Expand a Boot Disk on a GCE Instance

Google now allows you specify the size of your boot disk larger than 10GB when you create your instance. In any case, if you need to resize your boot disk for any reason, these are the steps I followed.

Here I’ve attached a 250GB blank disk to the instance:

Disk /dev/sda: 10.7 GB, 10737418240 bytes
4 heads, 32 sectors/track, 163840 cylinders, total 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x000ca37e
 Device Boot Start End Blocks Id System
/dev/sda1 * 2048 20971519 10484736 83 Linux


Disk /dev/sdb: 268.4 GB, 268435456000 bytes
255 heads, 63 sectors/track, 32635 cylinders, total 524288000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000
Disk /dev/sdb doesn't contain a valid partition table

sudo apt-get install pv
dd if=/dev/sda bs=64K | pv | dd of=/dev/sdb bs=64K

“pv” gives you a progress of the “dd” command. This will take some time. Once it’s finished:

10GB 0:03:43 [45.7MB/s] [ <=> ]
163840+0 records in
163840+0 records out
10737418240 bytes (11 GB) copied, 223.898 s, 48.0 MB/s
163840+0 records in
163840+0 records out
10737418240 bytes (11 GB) copied, 227.444 s, 47.2 MB/s

Now we re-partition the disk:

sudo fdisk /dev/sdb
hit "p" to list the partition.
hit "d" to delete the partition.
hit "n" for new partition. 
hit "p" for primary
hit "1" for partition number. 
enter the first section ("Start" from the "p" command above). In this case it was "2048"
For last sector, just press enter to max it out. 

Select partition number "1" 
hit "w" for write.

Now you could run:

e2fsck -f /dev/sdb1
resize2fs /dev/sdb1

1. Detach the disk,
2. Clone the instance and choose this disk as the root disk.
3. SSH and make sure everything looks good.

   Disk /dev/sda: 268.4 GB, 268435456000 bytes
   4 heads, 32 sectors/track, 4096000 cylinders, total 524288000 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 4096 bytes
   I/O size (minimum/optimal): 4096 bytes / 4096 bytes
   Disk identifier: 0x000ca37e
    Device Boot Start End Blocks Id System
   /dev/sda1 * 2048 524287999 262142976 83 Linux
   
   df -h
   
   Filesystem Size Used Avail Use% Mounted on
   /dev/sda1 247G 9.1G 225G 4% /
   none 4.0K 0 4.0K 0% /sys/fs/cgroup
   udev 1.8G 8.0K 1.8G 1% /dev
   tmpfs 371M 332K 370M 1% /run
   none 5.0M 0 5.0M 0% /run/lock
   none 1.9G 0 1.9G 0% /run/shm
   none 100M 0 100M 0% /run/user

4. Once it looks good, you could delete the original instance and create a new instance with this disk.