Monday 3 August 2015

Fail: AWS EFS (Preview) on AWS EC2 Windows Instance

Gah! :( Poor show this morning.

Was hoping to write up a disk performance comparison of AWS EFS against EBS on Windows. Alas it wasn't to be. I am still writing this failure up as it may be useful to someone, but this story doesn't have a happy ending.

TL;DR; AWS EFS and Windows Server 2012+ are very incompatible due to lack of NFSv4 compatibility

I was aware of the limited NFS version support by AWS (i.e. only 4, whilst Windows only supports 2, 3 and 4.1). Yet, I wanted to see what could be done. Plus, it all works fine in Linux. Let's walk through it.

AWS Elastic File System

After the AWS Summit this year, which I was disappointed I couldn't attend, I was lucky enough to attend a replay at Amazon's offices at the beginning of June in London. During it, I got to hear about the Elastic File System preview. It was billed as the missing link in the AWS cloud storage offering, allowed flexible storage options to be delivered and charged without having to re-provision storage or manually add another NAS drive.

Creating and mounting the EFS storage instance in Linux is easy enough. It's still in preview in the US-West region (Oregon).

1. Walk through the EFS wizard to create your EC2 instance. Amazon recommend creating this across all the availability zones in a region. You certainly don't have to, especially as they are charged at 30 cents (roughly 18.75p) per GB-month.

AWS Elastic File System (EFS)
2. Set the security groups on mount points. It's important to note that the security groups will manage the connection between the EFS mount point and the EC2 instance you'll create.

Adding Mount point security groups

3. Spin the shizzle! Note, the full creation process can take about 5 minutes before finally marking the EFS volume as available.
When created, it's still spinning up

Creating the mount points

4. Add the NFS port (2049) to the security group in the usual manner.

5. It was at the point of spinning up and logging in to a Windows EC2 instance that the process went wrong. You could reach the mount point through the IP address. You could also use the 'net use' command to access the NFS volume using the IP address. However, despite the picture below, you couldn't write anything to it. Hence, I couldn't really test it, let along run the performance tests on it.

All the utilities, excited and ready to run :)

6. In order to test whether it was me, I decided to spin up a Linux instance to try to access the NFS volume. I'd do this to check if I could access it from there, create a file and read it on the Windows server. The first part of that went without a hitch.

  1. Spin up the EC2 instance
  2. Add the EC2 Instance's security group to the EFS mount points' security group (The screen is the same as shown above) 
  3. Create a private key using puttyGen from 
  4. Access it using the AWS Linux ec2-user via Putty
  5. Install the NFSv4 client package into the AWS Linux instance using yum via an elevated command > "sudo yum install nfs-utils"
  6. Create directory to mount it to
  7. Mount the file system onto that directory using "mount -t nfs4 <mount>:/ /<directory>" 
Voila! Perfect!

connecting to AWS Linux instance via Putty

NFS4 installed using Yum

The only other thing I did was chmod the directory to get access (you can take ownership of it as well) and I touched a file into the directory and sure enough...

Windows fail! :(

So side-by-side. You can see Linux and Windows don't have the same access. Refreshing or reconnecting makes no difference in Windows. I changed access to the file to everyone and still no luck. However, Linux had absolutely no issues. Just for fun, I removed the security group access and tested the mounting again and it worked fine to block access.

When you've not set security group on EFS mount points


At the time of writing (08/2015) this issue arises from the annoying lack of [free] support from Microsoft for NFSv4 and the choice by AWS to only support NFSv4 (the only version Windows doesn't support). Here I have to be honest, I don't know which is worse. Whilst there is the possibility this could be shared across a Samba connection, you've got to then run an EC2 instance just to do that and this will increase latency. I'd definitely say that this product isn't ready to take share from Microsoft in this arena in the enterprise, though of course it works on Linux based environment perfectly well. 

The product will continue to mature I'm sure. However, I'll have to put my Windows performance investigation on hold for now sadly.


  1. Now deploy another Linux Instance, install CTDB on both, then share the mount via SAMBA to Windows.. Voila! AWS EFS on Windows. From me, to the world.. You are welcome :)

    1. Only just caught this (several months later). Thanks. I'll have my cluster up and running in no time :-D

  2. The performance of samba share backed by EFS is horrid to say the least. 60+ seconds to literally do anything. Do not use samba backed by EFS, it is unusable.


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