[CentOS-virt] CentOS Images on AWS with partitions on /dev/xvda1 are awkwared to resize

Thu Apr 30 03:33:51 UTC 2015
Kelly Prescott <kprescott at coolip.net>

to follow-up, I will give an example.
Here is the listing for the official centos AMI:

IMAGE   ami-96a818fe    aws-marketplace/CentOS 7 x86_64 (2014_09_29) EBS 
aws-marketplace available       public  [marketplace: 
aw0evgkw8e5c1q413zgy5pjce]        x86_64  machineebs      hvm     xen
BLOCKDEVICEMAPPING      EBS     /dev/sda1               snap-591037fd   8 
false   standard                Not Encrypted
as you can see the block device mapping is by default set to 
BLOCKDEVICEMAPPING      EBS     /dev/sda1               snap-591037fd   8
false   standard                Not Encrypted

it is a standard volume, not encrypted, and 8 GB
my modification consists in adding this to my run command for my ami 
  -b /dev/sda1=snap-591037fd:20:false:gp2

I set the drive the same, the snapshot the same, and I give it 20GB 
instead of 8, I also use the gp2 type instead of the standard as well as 
telling it not to delete the volume when the instance terminates.

Hope this helps.

On Wed, 29 Apr 2015, Nico Kadel-Garcia wrote:

> I'm staring at the free CentOS images on AWS, and seeing that whoever
> set those up elected to use a partition for /dev/xvda1 rather than
> taking advantage of Amazon's tendency to use "/dev/xvda", "/dev/xvdb",
> etc. for each disk and use those directly as a file system.
> The result is that if you elect to allocate a larger base disk image,
> for example allocating 50 Gig to allow local home directories or space
> for "mock" or for bulky logs, and don't spend the time to select and
> allocate new disk images, it's awkward to simply expand the "/"
> partition. And with only 8 Gig allocated in the latest CentOS 6 images
> that I see in AWS, it's possible to get pretty pressed for space
> pretty quickly.
> Now, AWS published guidelines on manipulating partition size, and
> expanding a matching filesystem, but they're very clear to "unmount
> the parition before you touch it!!!" That's a bit difficult to unmount
> with a "/" partition, and they understandably don't have the kind of
> "boot from CD and work from the console" setup I'd normally use for
> that kind of work.
> So: why did the creators of that CentOS AMI elect to use such a small
> / partition? And how dangerous is it, with the system essentially
> idle, to use "parted" to expand the "/dev/xvda1" parition and then use
> "resize2fs" to expand the "/" file system while the system is alive?
> Note that, because I'm a complete weasel, I know at least one way
> around this: add a second disk, copy the OS to *that*, set grub to
> boot from the second disk, reboot from that, paritition the first disk
> as desired, copy the OS back, reset grub to boot from the first disk,
> and pray. I've had good success with the approach in the past, and
> have rebuilt rougly 15,000 Linux systems this way. But the work
> predates CentOS, and I dont't want to go through that again.
> So, has anyone resized "/" successfully and gracefully on AWS CentOS instances?
>                             Nico Kadel-Garcia
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