How to use the command 'zpool' (with examples)

The ‘zpool’ command is used to manage ZFS pools, which are storage pools created using the ZFS file system. ZFS is designed to be robust and reliable, and the ‘zpool’ command allows users to control and configure the pools in various ways.

Use case 1: Show the configuration and status of all ZFS zpools

Code:

zpool status

Motivation: This use case is useful to quickly get an overview of the configuration and status of all ZFS zpools on a system. It provides information such as the pool name, size, allocated space, and health status.

Explanation: The ‘zpool status’ command displays the configuration and status information of all ZFS zpools on the system.

Example output:

  pool: tank
 state: ONLINE
  scan: scrub repaired 0B in 0 days 00:01:23 with 0 errors on Sat Nov 20 10:00:01 2021
config:

        NAME        STATE     READ WRITE CKSUM
        tank        ONLINE       0     0     0
          raidz2-0  ONLINE       0     0     0
            disk1   ONLINE       0     0     0
            disk2   ONLINE       0     0     0
            disk3   ONLINE       0     0     0
            disk4   ONLINE       0     0     0

errors: No known data errors

Use case 2: Check a ZFS pool for errors

Code:

zpool scrub pool_name

Motivation: It is essential to regularly check the integrity of a ZFS pool to detect and repair any possible errors. The ‘zpool scrub’ command verifies the checksum of every block in the pool and reports any errors found.

Explanation: The ‘zpool scrub’ command checks a ZFS pool for errors by verifying the checksum of every block. The pool_name argument specifies the name of the pool to be checked.

Example output:

scrub: scrub in progress for pool_name, started date time, 0B scanned, 0 errors, 1h39m to go

Use case 3: List zpools available for import

Code:

zpool import

Motivation: This use case is helpful when you want to see a list of ZFS zpools that are available for import on the system. It allows you to identify and select the pool you wish to import.

Explanation: The ‘zpool import’ command without any arguments lists all the available zpools that can be imported on the system.

Example output:

   pool: tank
     id: 1234567890
  state: ONLINE
 action: The pool can be imported using its name or numeric identifier.

Use case 4: Import a zpool

Code:

zpool import pool_name

Motivation: When a zpool is created on one system, it can be imported on another system if needed. This use case allows you to import a specific zpool onto the system using its name.

Explanation: The ‘zpool import’ command followed by the pool_name argument imports the specified zpool onto the system.

Example output:

   pool: tank
     id: 1234567890
  state: ONLINE
   ...

Use case 5: Export a zpool

Code:

zpool export pool_name

Motivation: Exporting a zpool is necessary when you want to remove it from the system or transfer it to another system. This use case unmounts all the filesystems belonging to the zpool and prepares it for export.

Explanation: The ‘zpool export’ command followed by the pool_name argument unmounts all the filesystems within the specified zpool and prepares it for export.

Example output:

umount: /mnt: not a mountpoint

Use case 6: Show the history of all pool operations

Code:

zpool history pool_name

Motivation: This use case allows you to view the history of all the operations performed on a specific zpool. It can be useful for auditing purposes or troubleshooting.

Explanation: The ‘zpool history’ command followed by the pool_name argument displays the history of all pool operations, including creation, destruction, and modification.

Example output:

History for 'pool_name':
20100518.0040  create    pool_name  raidz2 sdb0 sdc0 sdd0 sde0
20100518.1600  scrub     pool_name  -
20100519.0311  destroy   pool_name  -

Use case 7: Create a mirrored pool

Code:

zpool create pool_name mirror disk1 disk2 mirror disk3 disk4

Motivation: Creating a mirrored pool provides data redundancy by storing multiple copies of the data on separate disks. This is important for ensuring data integrity and availability.

Explanation: The ‘zpool create’ command followed by the pool_name and disk arguments creates a mirrored pool using the specified disks.

Example output (for a pool named “tank” with two mirrored disk groups):

   pool: tank
     id: 1234567890
  state: ONLINE
...

Use case 8: Add a cache (L2ARC) device to a zpool

Code:

zpool add pool_name cache cache_disk

Motivation: Adding a cache device (L2ARC) to a zpool can improve its performance by caching frequently accessed data. This can speed up read operations and reduce latency.

Explanation: The ‘zpool add’ command followed by the pool_name, cache, and cache_disk arguments adds a cache device to the specified zpool.

Example output:

No output is displayed upon adding a cache device to a zpool, but it improves performance for subsequent read operations.

Conclusion:

The ‘zpool’ command is a powerful tool for managing ZFS pools. It provides a wide range of functionalities, including checking pool status, importing and exporting pools, creating mirrored pools, and adding cache devices. Understanding and utilizing these use cases can help users effectively manage their ZFS storage infrastructure.