Swap Partition on EC2 Ubuntu
Written on Wed, 15 February 2017If you have a case of having file system as btrfs, you will know that you can't have swap files on such systems. In such case, you probably need a partition. If you're running your server on AWS EC2, then you can even opt for having SSD as your swap partition, especially if your other EBS if on HDD.
Step 1: Create your EBS and attach it to your EC2 instance
You will have to create a new volume in your AWS console or via AWS API.
- Volume Type: GP2 or IO1
- You can usually settle for GP2, but if you need the extra performance boost, you can go IO1. If you still need better performance, you should just launch an EC2 instance that has more RAM. If you don't mind a performance hit, you can go for st1 or sc1.
- Size: 8GB
- More capacity if you find yourself needing more. Although keep in mind that if you need more than 2 times the size of your RAM, you might want to consider a better EC2 instance with more RAM instead. I'm going to assume in this tutorial that you are using 8GB RAM.
- Availability Zone: The one which your instance resides in
Once you have created your volume, you must attach it to your instance.
Step 2: Find your newly attached volume
You can find your newly attached volume with:
sudo lsblk
You should see a disk called xvdf, or another letter, that has 8G of space. In this tutorial, I'm assuming your disk is xvdf.
Step 3: Check for existing swap
In this tutorial, I'm assuming you have no swap.
You can check for existing swap with:
sudo swapon --show
If there is no output, that means you have no swap space currently.
You can verify no existing swap with:
free -h
If you see that swap has 0B, that means there is no active swap present in system.
Step 4: Making swap
Format your partition with:
sudo mkswap /dev/xvdf
You should see something like:
Setting up swapspace version 1, size = 8 GiB (8589930496 bytes)
no label, UUID=d3a23c79-5144-47fa-b422-885ebf63e2fc
Take note of your UUID. You will need it.
Step 5: Enabling swap on boot
You need to configure your fstab with the new swap partition.
echo 'UUID=d3a23c79-5144-47fa-b422-885ebf63e2fc none swap sw 0 0' | sudo tee -a /etc/fstab
Be sure to replace your UUID in this command.
Reboot your computer for swap to take effect.
reboot
Step 6: Check your new swap space
Run these commands to see that you have 8G for swap space.
sudo swapon --show
free -h
If you don't see your new swap space, something has gone wrong somewhere as you were following this tutorial.
Step 7: Configuring swappiness (Optional)
Swappiness is a parameter for the system to determine how often your system swaps data out of RAM to swap space. The values are represented from 0 to 100, in percentages. By default, the value is 60.
You must remember that a swap on HDD is time costly, while a swap in SSD is lifespan costly. Since I'm running a server, I would prefer a value closer to 0, only to use RAM when absolutely neccessary. In some use cases, using swap actually increases performance.
Choose your ideal percentage, then run the following:
sudo sysctl vm.swappiness=10
I chose 10 so that it will use swap sparingly.
To make this value permanent during reboots, open /etc/sysctl.conf:
sudo nano /etc/sysctl.conf
Then add the following at the bottom:
vm.swappiness=10
Conclusion
Having swap has many advantages. In some cases, it will safe a technician from certain doom due to application crashes.
For me, I managed to lower my operating cost of running instances in AWS. After all, if I don't mind a bit of performace hit from running swap in SSD. In return, I get to half the cost of the instance running cost.
If you're looking to have a swap file instead of a swap partition, check out my other tutorial.
