Metering objects Metered file system size Metering throughput

How Amazon EFS reports file system and object sizes

The following sections describe how Amazon EFS reports file system sizes, sizes of objects within a file system, and file system throughput.

Metering Amazon EFS file system objects

Objects that you can view in an Amazon EFS system include regular files, directories, symbolic links, and special files (FIFOs and sockets). Each of these objects is metered for 2 kibibytes (KiB) of metadata (for its inode) and one or more increments of 4 KiB of data. The following list explains the metered data size for different types of file system objects:

Regular files – The metered data size of a regular file is the logical size of the file rounded to the next 4-KiB increment, except that it might be less for sparse files.

A sparse file is a file to which data is not written to all positions of the file before its logical size is reached. For a sparse file, in some cases the actual storage used is less than the logical size rounded to the next 4-KiB increment. In these cases, Amazon EFS reports actual storage used as the metered data size.
Directories – The metered data size of a directory is the actual storage used for the directory entries and the data structure that holds them, rounded to the next 4-KiB increment. The metered data size doesn't include the actual storage used by the file data.
Symbolic links and special files – The metered data size for these objects is always 4 KiB.

When Amazon EFS reports the space used for an object, through the NFSv4.1 space_used attribute, it includes the object's current metered data size but not its metadata size. You can use two utilities for measuring the disk usage of a file, the du and stat utilities. Following is an example of how to use the du utility on an empty file that includes the -k option to return the output in kilobytes.


$ du -k file
4      file

Following example shows how to use the stat utility on an empty file to return the file's disk usage.


$ /usr/bin/stat --format="%b*%B" file | bc
4096

To measure the size of a directory, use the stat utility. Find the Blocks value, and then multiply that value by the block size. Following is an example of how to use the stat utility on an empty directory:


$ /usr/bin/stat --format="%b*%B" . | bc 
4096

Metered size of an Amazon EFS file system

The metered size of an Amazon EFS file system includes the sum of the sizes of all current objects in all of the EFS storage classes. The size of each object is calculated from a representative sampling of the size of the object during the metered hour, for example from 8 AM to 9 AM.

An empty file contributes 6 KiB (2 KiB metadata + 4 KiB data) to the metered size of a file system. Upon creation, a file system has a single empty root directory and therefore has a metered size of 6 KiB.

The metered sizes of a particular file system define the usage for which the owner account is billed for that file system for that hour.

Note

The computed metered size doesn't represent a consistent snapshot of the file system at any particular time during that hour. Instead, it represents the sizes of the objects that existed in the file system at varying times within each hour, or possibly the hour before it. These sizes are summed to determine the file system's metered size for the hour. The metered size of a file system is thus eventually consistent with the metered sizes of the objects stored when there are no writes to the file system.

You can see the metered size for an Amazon EFS file system in the following ways:

Using the describe-file-systems AWS CLI command and the DescribeFileSystem API operation, the response includes the following:
```
"SizeInBytes":{
            "Timestamp": 1403301078,
            "Value": 29313744866,
            "ValueInIA": 675432,
            "ValueInStandard": 29312741784
            "ValueInArchive": 327650
         }
```
Where the metered size of ValueInStandard is also used to determine your I/O throughput baseline and burst rates for file systems using the Bursting Throughput mode.
View the StorageBytes CloudWatch metric, which displays the total metered size of data in each storage classes. For more information about the StorageBytes metric, see CloudWatch metrics for Amazon EFS.
Run the df command in Linux at the terminal prompt of an EC2 instance.

Don't use the du command on the root of the file system for storage metering purposes because the response does not reflect the full set data used for metering your file system.

Note

The metered size of ValueInStandard is also used to determine your I/O throughput baseline and burst rates. For more information, see Bursting throughput.

Metering Infrequent Access and Archive storage classes

The EFS Infrequent Access (IA) and Archive storage classes are metered in 4 KiB increments and have a minimum billing charge per file of 128 KiB. IA and Archive file metadata (2 KiB per file) is always stored and metered in the Standard storage class. Support for files smaller than 128 KiB is only available for lifecycle policies updated on or after 12:00 PM PT, November 26, 2023. Data access for IA and Archive storage is metered in 128 KiB increments.

You can use the StorageBytes CloudWatch metric to view the metered size of data in each of the storage classes. The metric also displays the total number of bytes that are consumed by small-file rounding within the IA and Archive storage classes. For more information about viewing CloudWatch metrics, see Accessing CloudWatch metrics for Amazon EFS. For more information about the StorageBytes metric, see CloudWatch metrics for Amazon EFS.

Metering throughput

Amazon EFS meters the throughput for read requests at one-third the rate of the other file system I/O operations. For example, if you are driving 30 mebibytes per second (MiBps) of both read and write throughput, the read portion counts as 10 MiBps of effective throughput, the write portion counts as 30 MiBps, and the combined metered throughput is 40 MiBps. This combined throughput adjusted for consumption rates is reflected in the MeteredIOBytes CloudWatch metric.

Metering Elastic throughput

When Elastic throughput mode is enabled for a file system, you pay only for the amount of metadata and data read from or written to the file system. Amazon EFS file systems using Elastic throughput mode meter and bill metadata reads as read operations and metadata writes as write operations. Metadata operations are metered in 4 KiB increments and data operations are metered in 32 KiB increments.

Metering Provisioned throughput

For file systems that use Provisioned throughput mode, you pay only for the amount of time that throughput is enabled. Amazon EFS meters file systems with Provisioned throughput mode enabled once every hour. For metering when Provisioned throughput mode is set for less than one hour, Amazon EFS calculates the time-average using millisecond precision.

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Viewing storage class size