# `[efs]` section
Defines the configuration settings for the Amazon EFS that's mounted on the head and compute nodes. For more information, see [CreateFileSystem](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html) in the *Amazon EFS API Reference*.
To learn how to include Amazon EFS file systems in your cluster definition, see ``[cluster]` section` / ``efs_settings``.
To use an existing Amazon EFS file system for long-term permanent storage that's independent of the cluster life cycle, specify [`efs_fs_id`](#efs-efs-fs-id).
If you don't specify [`efs_fs_id`](#efs-efs-fs-id), AWS ParallelCluster creates the Amazon EFS file system from the `[efs]` settings when it creates the cluster and deletes the file system and data when the cluster is deleted.
For more information, see [Best practices: moving a cluster to a new AWS ParallelCluster minor or patch version](best-practices.md#best-practices-cluster-upgrades).
The format is `[efs efs-name]`. *efs-name* must start with a letter, contain no more than 30 characters, and only contain letters, numbers, hyphens (-), and underscores (\$1).
```
[efs customfs]
shared_dir = efs
encrypted = false
performance_mode = generalPurpose
```
**Topics**
+ [`efs_fs_id`](#efs-efs-fs-id)
+ [`efs_kms_key_id`](#efs-efs-kms-key-id)
+ [`encrypted`](#efs-encrypted)
+ [`performance_mode`](#efs-performance-mode)
+ [`provisioned_throughput`](#efs-provisioned-throughput)
+ [`shared_dir`](#efs-shared-dir)
+ [`throughput_mode`](#efs-throughput-mode)
## `efs_fs_id`
**(Optional)** Defines the Amazon EFS file system ID for an existing file system.
Specifying this option voids all other Amazon EFS options except for [`shared_dir`](cluster-definition.md#cluster-shared-dir).
If you set this option, it only supports the following types of file systems:
+ File systems that don't have a mount target in the stack's Availability Zone.
+ File systems that have an existing mount target in the stack's Availability Zone with both inbound and outbound NFS traffic allowed from `0.0.0.0/0`.
The sanity check for validating [`efs_fs_id`](#efs-efs-fs-id) requires the IAM role to have the following permissions:
+ `elasticfilesystem:DescribeMountTargets`
+ `elasticfilesystem:DescribeMountTargetSecurityGroups`
+ `ec2:DescribeSubnets`
+ `ec2:DescribeSecurityGroups`
+ `ec2:DescribeNetworkInterfaceAttribute`
To avoid errors, you must add these permissions to your IAM role, or set `sanity_check = false`.
**Important**
When you set a mount target with inbound and outbound NFS traffic allowed from `0.0.0.0/0`, it exposes the file system to NFS mounting requests from anywhere in the mount target's Availability Zone. AWS doesn't recommend creating a mount target in the stack's Availability Zone. Instead, let AWS handle this step. If you want to have a mount target in the stack's Availability Zone, consider using a custom security group by providing a [`vpc_security_group_id`](vpc-section.md#vpc-security-group-id) option under the [`[vpc]` section](vpc-section.md). Then, add that security group to the mount target and turn off `sanity_check` to create the cluster.
There is no default value.
```
efs_fs_id = fs-12345
```
[Update policy: If this setting is changed, the update is not allowed.](using-pcluster-update.md#update-policy-fail)
## `efs_kms_key_id`
**(Optional)** Identifies the AWS Key Management Service (AWS KMS) customer managed key to be used to protect the encrypted file system. If this is set, the [`encrypted`](#efs-encrypted) setting must be set to `true`. This corresponds to the [KmsKeyId](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html#efs-CreateFileSystem-request-KmsKeyId) parameter in the *Amazon EFS API Reference*.
There is no default value.
```
efs_kms_key_id = 1234abcd-12ab-34cd-56ef-1234567890ab
```
[Update policy: If this setting is changed, the update is not allowed.](using-pcluster-update.md#update-policy-fail)
## `encrypted`
**(Optional)** Indicates whether the file system is encrypted. This corresponds to the [Encrypted](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html#efs-CreateFileSystem-request-Encrypted) parameter in the *Amazon EFS API Reference*.
The default value is `false`.
```
encrypted = true
```
[Update policy: If this setting is changed, the update is not allowed.](using-pcluster-update.md#update-policy-fail)
## `performance_mode`
**(Optional)** Defines the performance mode of the file system. This corresponds to the [PerformanceMode](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html#efs-CreateFileSystem-request-PerformanceMode) parameter in the *Amazon EFS API Reference*.
Valid options are the following values:
+ `generalPurpose`
+ `maxIO`
Both values are case sensitive.
We recommend the `generalPurpose` performance mode for most file systems.
File systems that use the `maxIO` performance mode can scale to higher levels of aggregate throughput and operations per second. However, there's a trade-off of slightly higher latencies for most file operations.
After the file system is created, this parameter can't be changed.
The default value is `generalPurpose`.
```
performance_mode = generalPurpose
```
[Update policy: If this setting is changed, the update is not allowed.](using-pcluster-update.md#update-policy-fail)
## `provisioned_throughput`
**(Optional)** Defines the provisioned throughput of the file system, measured in MiB/s. This corresponds to the [ProvisionedThroughputInMibps](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html#efs-CreateFileSystem-response-ProvisionedThroughputInMibps) parameter in the *Amazon EFS API Reference*.
If you use this parameter, you must set [`throughput_mode`](#efs-throughput-mode) to `provisioned`.
The quota on throughput is `1024` MiB/s. To request a quota increase, contact Support.
The minimum value is `0.0` MiB/s.
```
provisioned_throughput = 1024
```
[Update policy: This setting can be changed during an update.](using-pcluster-update.md#update-policy-setting-supported)
## `shared_dir`
**(Required)** Defines the Amazon EFS mount point on the head and compute nodes.
This parameter is required. The Amazon EFS section is used only if [`shared_dir`](cluster-definition.md#cluster-shared-dir) is specified.
Don't use `NONE` or `/NONE` as the shared directory.
The following example mounts Amazon EFS at `/efs`.
```
shared_dir = efs
```
[Update policy: If this setting is changed, the update is not allowed.](using-pcluster-update.md#update-policy-fail)
## `throughput_mode`
**(Optional)** Defines the throughput mode of the file system. This corresponds to the [ThroughputMode](https://docs.aws.amazon.com/efs/latest/ug/API_CreateFileSystem.html#efs-CreateFileSystem-request-ThroughputMode) parameter in the *Amazon EFS API Reference*.
Valid options are the following values:
+ `bursting`
+ `provisioned`
The default value is `bursting`.
```
throughput_mode = provisioned
```
[Update policy: This setting can be changed during an update.](using-pcluster-update.md#update-policy-setting-supported)