What is the difference between disk allocation and disk usage?

This may be an alarming observation at first, but I assure you that everything is okay with your Linode. I'd like to assuage your concerns by explaining the difference between disk allocation and disk usage.

Disk allocation

Disk allocation refers to the total amount of SSD storage space your Linode plan offers. You may view the allocation of all of our plans under the "Storage" column of our Pricing page.

By default, our systems provision 512 MB of your plan's disk allocation towards your Linode's swap drive, which helps protect your Linode against out-of-memory errors. The rest of your plan's allocation goes towards your Linode's primary disk drive, where your operating system and applications reside.

This default arrangement will allocate 100% of your Linode's SSD disk space towards two drives, which reflects what you are seeing on the Disks/Configs tab of your Linode.

100% disk allocation is generally desirable: it means that your are maximizing the value of your Linode plan by presenting its entire SSD space allotment to your Linode. That said, it may be prudent to deallocate some of this space in case you need some flexibility with your disk space provisioning. You may adjust these allotment values by resizing your disk with these instructions:

• Resize a Linode Disk

Our Pricing page lists our plan's sizes in GB (gigabytes), while our disk resize utility uses MB (megabytes). To convert from GB to MB, multiply the GB value by 1024. To convert from MB to GB, simply do the reverse and divide the MB value by 1024.

When resizing your Linode's disks, you will first need to power off your Linode. However, you do not need to worry about losing any data when reducing the size of your disks: our systems will prevent you from resizing your disk if you attempt to resize it below its current disk usage.

By deallocating your Linode's disk utilization below 100%, you may create additional disks on your plan using this reclaimed allocation:

• Disks and Configuration Profiles - Creating a Blank Disk

When creating additional disks in this manner, you will need to make these disks visible to your Linode by assigning to them to the "Block Device Assignment" section of your Linode's configuration profile. You may read more about this process and configuration profiles more generally here:

• Disks and Configuration Profiles - Configuration Profiles

With disk allocation receiving fair treatment at this point, it is now time to cover disk usage.

Disk usage

While disk allocation represent how much of your Linode plan's SSD storage space is actively provisioned to your Linode, disk usage represents how much data is saved to your Linode's disk.

You may use the df -h command to view the usage of all of your Linode's disks. Here is an example of this output from one of my own Linodes:

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            480M     0  480M   0% /dev
tmpfs            99M  1.6M   98M   2% /run
/dev/sda        9.9G  5.3G  4.1G  57% /
tmpfs           494M     0  494M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           494M     0  494M   0% /sys/fs/cgroup
tmpfs            99M     0   99M   0% /run/user/1000
/dev/sdc        7.1G   17M  7.0G   1% /mnt/freespace
/dev/sdd        7.0G  6.9G     0 100% /mnt/OutOfRoom

This output shows that this Linode contain three disk drives with filesystems:

• /dev/sda, the Linode's main disk drive. You can tell that it is the main disk drive since it is mounted at /, the root directory path in Unix-like systems such as Linux.
• /dev/sdc, an additional disk drive mounted at /mnt/freespace.
• /dev/sdd, an additional disk drive mounted at /mnt/OutOfRoom.

(In case you're wondering about /dev/sdb, this device is the swap drive for this Linode. Since they do not contain file systems, swap drives may not appear in df output.)

The disk usage for each of these drives is listed under the Used column, while the remaining space appears under the Avail column. You may compare these values against the disk's total space under the Size column, which will closely match the disk's allocation as listed under the Linode's Disks/Configs tab in Cloud Manager. (Linux filesystems will likely reserve several MB from the disk's allocation for journaling purposes.)

It is good to pay attention to both these raw disk usage figures along with the Use% value. This example indicates the following information about this Linode's disks:

• /dev/sda, the Linode's main disk drive, is currently using 5.3 GB out of its 9.9 GB total. This translates to 57% disk usage, leaving 4.1 GB free.
• /dev/sdc is currently using just 17 MB out of its 7.1 GB total. This translates to 1% disk usage, leaving 7.0 GB free.
• /dev/sdd is currently using just 6.9 GB out of its 7.0 GB total. Despite the small rounding discrepancy, this disk is 100% full as indicated by the 0 listed as this disk's Avail value.

You will need to determine what represents a reasonable usage figure for your Linode's disks depending on its applications. However, in general, a disk that is filling up represents an administrative problem which should be resolved as soon as possible. You may find this Community post valuable for freeing up space on a disk that is filling up:

• My disk is filling up. How can I find the culprit?

Going further

I highly encourage you to review our entire documentation regarding disks and configuration profiles, since it covers a lot of territory that this Community Site post does not:

• Disks and Configuration Profiles

Additionally, it is worth knowing that the df command supports a number of output formats. -h outputs your disk usage in human-readable format, but you may also use -m for megabytes or -k for kilobytes (the default for df). Running man df on your Linode will show you additional options which may be specific to your Linode's operating system.

Conclusion

Disk allocation represents how much space is assigned to each of your Linode's drives, while disk usage represents how much data is consuming that space. Disk usage cannot exceed that disk's allocated space.

While it may be alarming to see that your your Linode has a disk allocation of 100%, this is usually desirable since it means that you are getting the maximum value for your Linode's plan. On the other hand, approaching 100% disk usage is a genuine cause for concern, since it may result in your Linode's applications not working as expected. If your disk usage is approaching 100%, you should look into your Linode's file system as soon as possible to see if you can free some space and maintain the smooth operation of your Linode's applications.

I hope that this guide helps clearly delineate the difference between disk allocation and usage for you. Please feel free to respond if you have any questions or additional information you'd like to share about this topic!