ZFS

ZFS

Pools

The Pools page is used to both create zpools and to cluster them to create a service. The main page shows the pools discovered on a local node:

In the above example pools pool1 and pool2 are both clustered and running on node-a, pool3 is an exported, unclustered pool and poollocal is only visible to node-a and therefore cannot be clustered.

Creating a Pool

To create a zpool click the + CREATE POOL button on the main pools page. You will then be presented with the pool configuration page:

Fill out the Pool name field and select the desired structure of the pool from the Pool Mode list. The cluster supports three types of layout when creating vdevs for a pool:

• raidz2 - Two of the drives are used as parity drives, meaning up to two drives can be lost in the vdev without impacting the pool. When striping raidz2 vdevs together each vdev can survive the loss of two of its members.
• mirror - Each drive in the vdev will be mirrored to another drive in the same vdev. Vdevs can then be striped together to build up a mirrored pool.
• jbod - Creates a simple pool of striped disks with no redundancy.

RAIDZ2 Pool

For this example a RAIDZ2 pool consisting of two five drive vdevs striped together, a log, a cache and a spare will be created. Five disks are selected for the first vdev, the desired Pool Name entered and raidz2 chosen from the Pool Mode list:

Click on DATA from the Add selected disks menu to configure the first vdev:

Next the second vdev is added, again using five drives, but this time selecting + New vdev from the DATA menu:

The resulting configuration depicts the two vdevs striped together:

Next a log disk is added by selecting one of the remaining available drives and clicking the LOG button:

The same is done for a cache and spare device giving the final configuration:

Finally click SUBMIT. The pool will now be created and will show up in the main pools page. Select the pool to show the pool details - device information can also be shown by clicking Show on the devices line:

Mirrored Pool

Mirrored pools are created by striping together individual mirrored vdevs.

Start by creating an individual mirrored vdev (in this example a two way mirror is created, but three, four way, etc. mirrors can be created if required):

Continue adding mirrored vdevs as required:

Finally click SUBMIT. The pool will now be created and will show up in the main pools page.

JBOD Pool (single stripe)

A jbod pool is a stripe of disks in a single vdev with no redundancy. Select individual disks and add them to the vdev using the data button:

Finally click SUBMIT. The pool will now be created and will show up in the main pools page.

Preparing a Pool to Cluster

Pools must be imported on one of the nodes before they can be clustered. Check their status by selecting the Pools option on the side menu.

In the following example pool1 and pool2 are already clustered and pool3 is going to be added to the cluster:

Firstly the pool need to be imported; select the Import Pool item from the Actions menu:

The status of the pool should now change to Imported and CLUSTERABLE:

The pool is now ready for clustering.

Clustering a Pool

Select the Cluster this pool item from the Actions menu:

Fill out the description and select the preferred node for the service:

With a shared-nothing pool the GUID's for each pool will be shown:

To add a virtual hostname to the service click Add in the Virtual Hostname panel. Enter the IP address, and optionally a hostname. For nodes with multiple network interfaces, use the drop down lists to select which interface the virtual hostname should be assigned to:

Finally, click the Create button; the pool will now show as CLUSTERED:

Datasets

Creating Datasets

ZFS uses datasets to organize and store data. A ZFS dataset is similar to a mounted filesystem and has its own set of properties, including a quota that limits the amount of data that can be stored. Datasets are organized in the ZFS hierarchy and can have different mountpoints.

The following steps will show the process of creating a dataset within clustered and non clustered pools.

1. To create a dataset navigate to ZFS -> Datasets and click CREATE DATASET:

   

2. Select the Parent Pool and enter a Dataset Name and set any options required:

   

   Available options:

   Option	Description
   Mountpoint path	Alternative path to mount the dataset or pool. Do not change the mountpoint of a clustered pool, doing this will break automatic failover
   Compression	Enable compression or select an alternative compression type (lz4/zstd) on - The current default compression algorithm will be used (does not select a fixed compression type; as new compression algorithms are added to ZFS and enabled on a pool, the default compression algorithm may change). off - No compression. lz4 - A high-performance compression and decompression algorithm, as well as a moderately higher compression ratio than the older lzjb (the original compression algorithm). zstd - Provides both high compression ratios and good performance and is preferable over lz4.
   Dataset Quota	Set a limit on the amount of disk space a file system can use.
   Reservation Size	Guarantee a specified amount of disk space is available to a file system.
   ACL Inherit	Setermine the behavior of ACL inheritance (i.e. how ACLs are inherited when files and directories are created). The following options are available: discard - No ACL entries are inherited. The file or directory is created according to the client and protocol being used. noallow - Only inheritable ACL entries specifying deny permissions are inherited. restricted - Removes the write_acl and write_owner permissions when the ACL entry is inherited, but otherwise leaves inheritable ACL entries untouched. This is the default. passthrough - All inheritable ACL entries are inherited. The passthrough mode is typically used to cause all data files to be created with an identical mode in a directory tree. An administrator sets up ACL inheritance so that all files are created with a mode, such as 0664 or 0666. passthrough-x - Same as passthrough except that the owner, group, and everyone ACL entries inherit the execute permission only if the file creation mode also requests the execute bit. The passthrough setting works as expected for data files, but you might want to optionally include the execute bit from the file creation mode into the inherited ACL. One example is an output file that is generated from tools, such as cc or gcc. If the inherited ACL does not include the execute bit, then the output executable from the compiler won't be executable until you use chmod(1) to change the file's permissions.
   ACL Mode	Modify ACL behavior whenever a file or directory's mode is modified by the chmod command or when a file is initially created. discard - All ACL entries are removed except for the entries needed to define the mode of the file or directory. groupmask - User or group ACL permissions are reduced so that they are no greater than the group permission bits, unless it is a user entry that has the same UID as the owner of the file or directory. Then, the ACL permissions are reduced so that they are no greater than owner permission bits. passthrough - During a chmod operation, ACEs other than owner@, group@, or everyone@ are not modified in any way. ACEs with owner@, group@, or everyone@ are disabled to set the file mode as requested by the chmod operation.
   User Ownership	Sets the ownership of the dataset
   Group Ownership	Sets the group ownership of the dataset
   Extended Attributes	Controls whether extended attributes are enabled for this file system. Two styles of extended attributes are supported: either directory-based or system-attribute-based. off - Extended attributes are disabled on - Extended attributes are enabled; the default value of on enables directory-based extended attributes. sa - System based attributes dir - Directory based attributes
   Enable NFS Share	enable NFS sharing dataset via ZFS. Do not enable if managing Shares via the WebApp.
   Enable SMB Share	enable SMB sharing dataset via ZFS. Do not enable if managing Shares via the WebApp.
   Update Access Time	controls whether the access time for files is updated on read.

   What is an ACL

   An ACL is a list of user permissions for a file, folder, or other data object. The entries in an ACL specify which users and groups can access something and what actions they may perform.

   What are Extended Attributes

   Extended file attributes are file system features that enable additional attributes to be associated with computer files as metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem.

   In ZFS directory based extended attributes (dir) imposes no practical limit on either the size or number of attributes which can be set on a file. Although under Linux the getxattr(2) and setxattr(2) system calls limit the maximum size to 64K. This is the most compatible style of extended attribute and is supported by all ZFS implementations.

   With system extended attributes (sa) the key advantage is improved performance. Storing extended attributes as system attributes significantly decreases the amount of disk I/O required. Up to 64K of data may be stored per-file in the space reserved for system attributes. If there is not enough space available for an extended attribute then it will be automatically written as a directory-based xattr. System-attribute-based extended attributes are not accessible on platforms which do not support the xattr=sa feature. OpenZFS supports xattr=sa on both FreeBSD and Linux.

3. Click SUBMIT to create - the Dataset is now created in the pool:

   

Modifying Datasets

To modify an existing dataset, click the button to the right of the dataset:

Deleting Datasets

To delete a dataset, click the button to the right of the dataset and confirm by clicking the REMOVE DATASET option.

Zvols

Creating Zvols

Zvols are block storage devices, cannot be mounted and primarily used for iSCSI backing stores. The size and compression used can be set for each individual backing store.

The following steps will show the process of creating a zvol within clustered and non clustered pools.

1. To create a zvol navigate to ZFS -> Zvols and click CREATE ZVOL:

   

2. Select the Parent Pool and enter a Zvol Name and set any options required:

   

   Available options:

   Option	Description
   Zvols size	Size of the zvol to create - can be specified in units of KB, MB, GB, TB and PB
   Compression	Enable compression or select an alternative compression type (lz4/zstd) on - The current default compression algorithm will be used (does not select a fixed compression type; as new compression algorithms are added to ZFS and enabled on a pool, the default compression algorithm may change). off - No compression. lz4 - A high-performance compression and decompression algorithm, as well as a moderately higher compression ratio than the older lzjb (the original compression algorithm). zstd - Provides both high compression ratios and good performance and is preferable over lz4.

3. Click SUBMIT to create - the Zvol is now created in the pool.

   

Modifying Zvols

To modify an existing zvol, click the button to the right of the zvol:

Deleting Zvols

To delete a zvol, click the button to the right of the zvol and confirm by clicking the REMOVE ZVOL option.

Snapshots

Creating Snapshots

A zfs snapshot is a read-only copy of a ZFS dataset or zvol. Snapshots are created almost instantly and initially consume no additional disk space within the pool. They are a valuable tool both for system administrators needing to perform backups and other users who need to save the state of their file system at a particular point in time and possibly restore it later. It is also possible to extract individual files from a snapshot.

The following steps will show the process of creating a snapshot from a clustered pool.

1. To create a snapshot navigate to ZFS -> Snapshots and click CREATE SNAPSHOT:

   

2. Select the Pool Name and the Dataset within the pool (set this field to None to snapshot the whole of the selected pool). Finally specify a snapshot name and click SUBMIT:

   Snapshot name

   The cluster software automatically prefixes the snapshot name with pool/dataset name followed by the '@' symbol. Therefore when entering a snapshot name the '@' symbol cannot be used.

   

3. Click SUBMIT to create - the Zvol is now created in the pool.

   

Restoring Snapshots

Restoring a snapshot will revert the dataset/pool back to the position it was in when the snapshot was taken. This process is known as rolling back.

Deleting Snapshots

Use the DELETE button to remove a snapshot. Once removed any space used by the snapshot will be recovered.