Now, that additional 60GB isn't exactly going to break the bank (it works out at about £50 per year) however I'm committed to provisioning the correct size.
I investigated a few different options for shrinking the Windows boot drive in AWS and this is the one that I found to be the most clear.
In this walkthrough I'll be working on hostname DC01 as the Windows machine in question
AWS Console
- Take a snapshot of DC01
Windows
- Start -> Administrative Tools -> Computer Management -> Storage -> Disk Management
- Right-click on Volume C: -> Shrink Volume so the 'Total size after shrink' is no more than 39000 MB
- Start -> Shut down.
AWS Console
- Determine which Availability Zone DC01 is in. In this case it's zone 1a in eu-west:
- Create a new Amazon Linux EC2 instance in the same zone.
- I chose an EBS-optimised m1.large to improve the disk speed
- Detach the 100GB root volume from DC01
- Attach the 100GB root volume to the new Amazon Linux EC2 instance as device /dev/sdf (the default as of writing)
- Create a new 40GB standard EBS volume in the same zone and attach it to the Amazon Linux EC2 instance as device /dev/sdg (be careful - it defaults to /dev/sdf)
Amazon Linux EC2 instance
- Check that the devices are mounted correctly with 'fdisk':
- Yes, /dev/sdf is our 100G source drive and /dev/sdg is the new 40G destination
- Use 'dd' to copy the contents of the source to the destination
- dd if=/dev/sdf of=/dev/sdg bs=1M
- The 'bs=1M' tells dd to use a block size of one megabyte - this is not only faster but also reduces the number of I/O operations. AWS charges per I/O operation :)
- BONUS: this will also do a full block format to maximise EBS performance
- The 'no space left on device' message is perfectly normal - 100GB of data will not fit into 40GB - the important part is the useful data is occupying less than 40GB
AWS Console
- Stop the Amazon Linux EC2 instance
- Detach both the 100G and 40G volumes
- Attach the 40G volume as device /dev/sda1 of DC01
- Start DC01
Windows
- Verify that the instance comes up and the root device is 40GB as expected:
AWS Console
- delete the 100GB snapshot
- delete the 100GB original volume from DC01
- terminate the Amazon Linux EC2 instance
Tada!
Hello Gavin, thanks a lot for yout post, very simple to follow.
ReplyDeleteIn appreciation for your generous post I will try to humbly complement somethings that arrised to me when following your instructions:
* Some custom linux kernels do not use names like "/dev/sdf" for the volumes, so if you put those names in the EC2 Management Console, the linux box instead will use names like "/dev/xvdf". Use a simple "mount" command at the linux box to know what type or kernel you have when attaching the volumnes (so you are secure of what results you will get when following Gavin instructions). This issue is documented in the EC2 User Guide in the Storage chapter.
* The "dd" command may take very long time to copy the volume, and you as the user will look for a way to enquire about the progress of the copy operation. A simple way could be with the command:
% sudo kill -USR1 >pid of dd<
from another linux command shell. Get the process id with a command like
% ps -ef | grep dd
This won´t kill the dd process, it will send it a signal, seconds later from issuing the signal, dd will report its progress, with a format like:
0+14 records in
0+14 records out
204 bytes (204 B) copied, 24.92 seconds, 0.0 kB/s
I used it after waiting 3 hours for the completion of the copy with dd. Obviously I was worried about the succes of the copy operation.
I hope this helps and make your post even more usefull.
Regards,
Eduardo Yánez.
Hey Eduardo,
DeleteMany thanks for your kind words about the blog post and also for your follow-up improvements. You're right about the device letters - certainly the classic 'sd' device names in the Amazon Linux AMI are just symlinks to the real block devices on /dev/xvdN:
[root@ip-10-0-0-181 ~]# ls -l /dev/sda1
lrwxrwxrwx 1 root root 5 Oct 10 12:08 /dev/sda1 -> xvda1
[root@ip-10-0-0-181 ~]# ls -l /dev/xvda1
brw-rw---- 1 root disk 202, 1 Oct 10 12:08 /dev/xvda1
On the topic of 'dd' progress, I often tend to open another PuTTY window and just run 'vmstat 5' to see the 'bi' and 'bo' columns telling me how quickly the transfer progress is running.
The great thing about Linux (and any OS, really..) is there are so many different ways to solve the same problem! :)
Cheers,
Gavin.
For the non-linux guys out there, there is a way to do it and stay within Windows. Please see the technical article on my Evernote account here: https://www.evernote.com/shard/s2/sh/2801b360-994c-4b6e-8aab-3743f9662fe9/7403918691bb67b82fc20310a71bab0a
ReplyDeleteI had been looking for a method for shrinking Windows root volumes in AWS for quite a while and your works like a charm. Thank you Gavin!
ReplyDeleteYou need to run the dd command using sudo.
ReplyDeleteAlso to get the status, run this command in another shell prompt and view the result in the first shell prompt:
Deletesudo kill -USR1 $(pgrep ^dd)
or even (to get status updates every 60 seconds):
Deleteuntil [ ! $(pgrep ^dd) ]; do sudo kill -USR1 $(pgrep ^dd) && sleep 60; done
Hi Gavin,
ReplyDeleteThanks so much for the walk-through. Very easy to follow and worked like a charm!
An observation, though. Contrary to ~3hrs reported by Eduardo Yánez, it took less than 30mins to shrink a 200GB Windows instance to 50GB using m1.large, you suggested. (Amazon might be much more faster, nowadays).
Thanks once again for saving me hundred of bucks!
Regards,
ADEBISI Foluso.
Excellent. Works great.
ReplyDeleteGreat! Thanks for the detailed instructions. It works.
ReplyDeleteThank you. It worked!
ReplyDeletedd is wonderful as it will do block level copies, etc. However as noted here it will run until there is no more disk space (40GB disk) to write to. Fine. What if there are data on the original 100GB volume that is located AFTER the 40GB mark. You will be in a load of hurt (missing/corrupt files). Disk defrag'ing and making sure all data are within the first 39GB of the original 100GB drive would be necessary
ReplyDeleteHi Charles,
DeleteThanks for the comments - if you have a look at the article again, you'll see there is a dedicated step (the second screenshot) for shrinking the volume size below 40GB. The 'dd' is just to copy that remaining portion.
Cheers,
Gavin.
YES!
Deletethanks for re-pointing that out to me. That is something I over-looked.
Cheers
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