Chapter 17. Managing layered local storage with Stratis

You can easily set up and manage complex storage configurations integrated by the Stratis high-level system.

Important

Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.

17.1. Setting up Stratis file systems

As a system administrator, you can enable and set up the Stratis volume-managing file system on your system to easily manage layered storage.

17.1.1. The purpose and features of Stratis

Stratis is a local storage-management solution for Linux. It is focused on simplicity and ease of use, and gives you access to advanced storage features.

Stratis makes the following activities easier:

  • Initial configuration of storage
  • Making changes later
  • Using advanced storage features

Stratis is a hybrid user-and-kernel local storage management system that supports advanced storage features. The central concept of Stratis is a storage pool. This pool is created from one or more local disks or partitions, and volumes are created from the pool.

The pool enables many useful features, such as:

  • File system snapshots
  • Thin provisioning
  • Tiering

17.1.2. Components of a Stratis volume

Externally, Stratis presents the following volume components in the command-line interface and the API:

blockdev
Block devices, such as a disk or a disk partition.
pool

Composed of one or more block devices.

A pool has a fixed total size, equal to the size of the block devices.

The pool contains most Stratis layers, such as the non-volatile data cache using the dm-cache target.

Stratis creates a /stratis/my-pool/ directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.

filesystem

Each pool can contain one or more file systems, which store files.

File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.

The file systems are formatted with XFS.

Important

Stratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.

Stratis creates links to file systems at the /stratis/my-pool/my-fs path.

Note

Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.

17.1.3. Block devices usable with Stratis

This section lists storage devices that you can use for Stratis.

Supported devices

Stratis pools have been tested to work on these types of block devices:

  • LUKS
  • LVM logical volumes
  • MD RAID
  • DM Multipath
  • iSCSI
  • HDDs and SSDs
  • NVMe devices
Warning

In the current version, Stratis does not handle failures in hard drives or other hardware. If you create a Stratis pool over multiple hardware devices, you increase the risk of data loss because multiple devices must be operational to access the data.

Unsupported devices

Because Stratis contains a thin-provisioning layer, Red Hat does not recommend placing a Stratis pool on block devices that are already thinly-provisioned.

Additional resources

  • For iSCSI and other block devices requiring network, see the systemd.mount(5) man page for information on the _netdev mount option.

17.1.4. Installing Stratis

This procedure installs all packages necessary to use Stratis.

Procedure

  1. Install packages that provide the Stratis service and command-line utilities: 

    # yum install stratisd stratis-cli

  2. Make sure that the stratisd service is enabled: 

    # systemctl enable --now stratisd

17.1.5. Creating a Stratis pool

This procedure describes how to create an encrypted or an unencrypted Stratis pool from one or more block devices.

The following notes apply to encrypted Stratis pools:

  • Each block device is encrypted using the cryptsetup library and implements the LUKS2 format.
  • Each Stratis pool can have a unique key or it can share the same key with other pools. These keys are stored in the kernel keyring.
  • All block devices that comprise a Stratis pool are either encrypted or unencrypted. It is not possible to have both encrypted and unencrypted block devices in the same Stratis pool.
  • Block devices added to the data tier of an encrypted Stratis pool are automatically encrypted.

Prerequisites

  • Stratis v2.2.1 is installed on your system. See Section 17.1.4, “Installing Stratis”.
  • The stratisd service is running.
  • The block devices on which you are creating a Stratis pool are not in use and are not mounted.
  • The block devices on which you are creating a Stratis pool are at least 1 GiB in size each.

  • On the IBM Z architecture, the /dev/dasd* block devices must be partitioned. Use the partition in the Stratis pool.

    For information on partitioning DASD devices, see Configuring a Linux instance on IBM Z.

Procedure

  1. If the selected block device contains file system, partition table, or RAID signatures, erase them using the following command: 

    # wipefs --all block-device

    where block-device is the path to the block device; for example, /dev/sdb.

  2. Create the new Stratis pool on the selected block device(s):

    Note

    Specify multiple block devices on a single line, separated by a space: 

    # stratis pool create my-pool block-device-1 block-device-2

    • To create an unencrypted Stratis pool, use the following command and go to step 3: 

      # stratis pool create my-pool block-device

      where block-device is the path to an empty or wiped block device.

      Note

      You cannot encrypt an unencrypted Stratis pool after you create it.

    • To create an encrypted Stratis pool, complete the following steps:

      1. If you have not created a key set already, run the following command and follow the prompts to create a key set to use for the encryption: 

        # stratis key set --capture-key key-description

        where key-description is the description or name of the key set.

      2. Create the encrypted Stratis pool and specify the key description to use for the encryption. You can also specify the key path using the --keyfile-path parameter instead. 

        # stratis pool create --key-desc key-description my-pool block-device

        where

        key-description
        Specifies the description or name of the key file to be used for the encryption.
        my-pool
        Specifies the name of the new Stratis pool.
        block-device
        Specifies the path to an empty or wiped block device.

  3. Verify that the new Stratis pool was created: 

    # stratis pool list

Troubleshooting

After a system reboot, sometimes you might not see your encrypted Stratis pool or the block devices that comprise it. If you encounter this issue, you must unlock the Stratis pool to make it visible.

To unlock the Stratis pool, complete the following steps:

  1. Recreate the key set using the same key description that was used previously: 

    # stratis key set --capture-key key-description

  2. Unlock the Stratis pool and the block device(s): 

    # stratis pool unlock

  3. Verify that the Stratis pool is visible: 

    # stratis pool list

Additional resources

  • The stratis(8) man page.

Next steps

17.1.6. Creating a Stratis file system

This procedure creates a Stratis file system on an existing Stratis pool.

Prerequisites

Procedure

  1. To create a Stratis file system on a pool, use: 

    # stratis fs create my-pool my-fs
    • Replace my-pool with the name of your existing Stratis pool.
    • Replace my-fs with an arbitrary name for the file system.

  2. To verify, list file systems within the pool: 

    # stratis fs list my-pool

Additional resources

  • The stratis(8) man page

Next steps

17.1.7. Mounting a Stratis file system

This procedure mounts an existing Stratis file system to access the content.

Prerequisites

Procedure

  • To mount the file system, use the entries that Stratis maintains in the /stratis/ directory: 

    # mount /stratis/my-pool/my-fs mount-point

The file system is now mounted on the mount-point directory and ready to use.

Additional resources

  • The mount(8) man page

17.1.8. Persistently mounting a Stratis file system

This procedure persistently mounts a Stratis file system so that it is available automatically after booting the system.

Prerequisites

Procedure

  1. Determine the UUID attribute of the file system: 

    $ lsblk --output=UUID /stratis/my-pool/my-fs

    For example:

    Example 17.1. Viewing the UUID of Stratis file system

    $ lsblk --output=UUID /stratis/my-pool/fs1

UUID
a1f0b64a-4ebb-4d4e-9543-b1d79f600283

  2. If the mount point directory does not exist, create it: 

    # mkdir --parents mount-point

  3. As root, edit the /etc/fstab file and add a line for the file system, identified by the UUID. Use xfs as the file system type and add the x-systemd.requires=stratisd.service option.

    For example:

    Example 17.2. The /fs1 mount point in /etc/fstab

    UUID=a1f0b64a-4ebb-4d4e-9543-b1d79f600283 /fs1 xfs defaults,x-systemd.requires=stratisd.service 0 0

  4. Regenerate mount units so that your system registers the new configuration: 

    # systemctl daemon-reload

  5. Try mounting the file system to verify that the configuration works: 

    # mount mount-point

Additional resources

17.2. Extending a Stratis volume with additional block devices

You can attach additional block devices to a Stratis pool to provide more storage capacity for Stratis file systems.

17.2.1. Components of a Stratis volume

Externally, Stratis presents the following volume components in the command-line interface and the API:

blockdev
Block devices, such as a disk or a disk partition.
pool

Composed of one or more block devices.

A pool has a fixed total size, equal to the size of the block devices.

The pool contains most Stratis layers, such as the non-volatile data cache using the dm-cache target.

Stratis creates a /stratis/my-pool/ directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.

filesystem

Each pool can contain one or more file systems, which store files.

File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.

The file systems are formatted with XFS.

Important

Stratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.

Stratis creates links to file systems at the /stratis/my-pool/my-fs path.

Note

Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.

17.2.2. Adding block devices to a Stratis pool

This procedure adds one or more block devices to a Stratis pool to be usable by Stratis file systems.

Prerequisites

  • Stratis is installed. See Section 17.1.4, “Installing Stratis”.
  • The stratisd service is running.
  • The block devices that you are adding to the Stratis pool are not in use and not mounted.
  • The block devices that you are adding to the Stratis pool are at least 1 GiB in size each.

Procedure

  • To add one or more block devices to the pool, use: 

    # stratis pool add-data my-pool device-1 device-2 device-n

Additional resources

  • The stratis(8) man page

17.3. Monitoring Stratis file systems

As a Stratis user, you can view information about Stratis volumes on your system to monitor their state and free space.

17.3.1. Stratis sizes reported by different utilities

This section explains the difference between Stratis sizes reported by standard utilities such as df and the stratis utility.

Standard Linux utilities such as df report the size of the XFS file system layer on Stratis, which is 1 TiB. This is not useful information, because the actual storage usage of Stratis is less due to thin provisioning, and also because Stratis automatically grows the file system when the XFS layer is close to full.

Important

Regularly monitor the amount of data written to your Stratis file systems, which is reported as the Total Physical Used value. Make sure it does not exceed the Total Physical Size value.

Additional resources

  • The stratis(8) man page

17.3.2. Displaying information about Stratis volumes

This procedure lists statistics about your Stratis volumes, such as the total, used, and free size or file systems and block devices belonging to a pool.

Prerequisites

Procedure

  • To display information about all block devices used for Stratis on your system: 

    # stratis blockdev

Pool Name  Device Node    Physical Size   State  Tier
my-pool    /dev/sdb            9.10 TiB  In-use  Data

  • To display information about all Stratis pools on your system: 

    # stratis pool

Name    Total Physical Size  Total Physical Used
my-pool            9.10 TiB              598 MiB

  • To display information about all Stratis file systems on your system: 

    # stratis filesystem

Pool Name  Name  Used     Created            Device
my-pool    my-fs 546 MiB  Nov 08 2018 08:03  /stratis/my-pool/my-fs

Additional resources

  • The stratis(8) man page

17.4. Using snapshots on Stratis file systems

You can use snapshots on Stratis file systems to capture file system state at arbitrary times and restore it in the future.

17.4.1. Characteristics of Stratis snapshots

This section describes the properties and limitations of file system snapshots on Stratis.

In Stratis, a snapshot is a regular Stratis file system created as a copy of another Stratis file system. The snapshot initially contains the same file content as the original file system, but can change as the snapshot is modified. Whatever changes you make to the snapshot will not be reflected in the original file system.

The current snapshot implementation in Stratis is characterized by the following:

  • A snapshot of a file system is another file system.
  • A snapshot and its origin are not linked in lifetime. A snapshotted file system can live longer than the file system it was created from.
  • A file system does not have to be mounted to create a snapshot from it.
  • Each snapshot uses around half a gigabyte of actual backing storage, which is needed for the XFS log.

17.4.2. Creating a Stratis snapshot

This procedure creates a Stratis file system as a snapshot of an existing Stratis file system.

Prerequisites

Procedure

  • To create a Stratis snapshot, use: 

    # stratis fs snapshot my-pool my-fs my-fs-snapshot

Additional resources

  • The stratis(8) man page

17.4.3. Accessing the content of a Stratis snapshot

This procedure mounts a snapshot of a Stratis file system to make it accessible for read and write operations.

Prerequisites

Procedure

  • To access the snapshot, mount it as a regular file system from the /stratis/my-pool/ directory: 

    # mount /stratis/my-pool/my-fs-snapshot mount-point

Additional resources

17.4.4. Reverting a Stratis file system to a previous snapshot

This procedure reverts the content of a Stratis file system to the state captured in a Stratis snapshot.

Prerequisites

Procedure

  1. Optionally, back up the current state of the file system to be able to access it later: 

    # stratis filesystem snapshot my-pool my-fs my-fs-backup

  2. Unmount and remove the original file system: 

    # umount /stratis/my-pool/my-fs
# stratis filesystem destroy my-pool my-fs

  3. Create a copy of the snapshot under the name of the original file system: 

    # stratis filesystem snapshot my-pool my-fs-snapshot my-fs

  4. Mount the snapshot, which is now accessible with the same name as the original file system: 

    # mount /stratis/my-pool/my-fs mount-point

The content of the file system named my-fs is now identical to the snapshot my-fs-snapshot.

Additional resources

  • The stratis(8) man page

17.4.5. Removing a Stratis snapshot

This procedure removes a Stratis snapshot from a pool. Data on the snapshot are lost.

Prerequisites

Procedure

  1. Unmount the snapshot: 

    # umount /stratis/my-pool/my-fs-snapshot

  2. Destroy the snapshot: 

    # stratis filesystem destroy my-pool my-fs-snapshot

Additional resources

  • The stratis(8) man page

17.5. Removing Stratis file systems

You can remove an existing Stratis file system or a Stratis pool, destroying data on them.

17.5.1. Components of a Stratis volume

Externally, Stratis presents the following volume components in the command-line interface and the API:

blockdev
Block devices, such as a disk or a disk partition.
pool

Composed of one or more block devices.

A pool has a fixed total size, equal to the size of the block devices.

The pool contains most Stratis layers, such as the non-volatile data cache using the dm-cache target.

Stratis creates a /stratis/my-pool/ directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.

filesystem

Each pool can contain one or more file systems, which store files.

File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.

The file systems are formatted with XFS.

Important

Stratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.

Stratis creates links to file systems at the /stratis/my-pool/my-fs path.

Note

Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.

17.5.2. Removing a Stratis file system

This procedure removes an existing Stratis file system. Data stored on it are lost.

Prerequisites

Procedure

  1. Unmount the file system: 

    # umount /stratis/my-pool/my-fs

  2. Destroy the file system: 

    # stratis filesystem destroy my-pool my-fs

  3. Verify that the file system no longer exists: 

    # stratis filesystem list my-pool

Additional resources

  • The stratis(8) man page

17.5.3. Removing a Stratis pool

This procedure removes an existing Stratis pool. Data stored on it are lost.

Prerequisites

Procedure

  1. List file systems on the pool: 

    # stratis filesystem list my-pool

  2. Unmount all file systems on the pool: 

    # umount /stratis/my-pool/my-fs-1 \
         /stratis/my-pool/my-fs-2 \
         /stratis/my-pool/my-fs-n

  3. Destroy the file systems: 

    # stratis filesystem destroy my-pool my-fs-1 my-fs-2

  4. Destroy the pool: 

    # stratis pool destroy my-pool

  5. Verify that the pool no longer exists: 

    # stratis pool list

Additional resources

  • The stratis(8) man page