--- category: tool tool: ZFS contributors: - ["sarlalian", "http://github.com/sarlalian"] - ["81reap", "https://github.com/81reap"] - ["A1EF", "https://github.com/A1EF"] filename: LearnZfs.txt --- [ZFS](http://open-zfs.org/wiki/Main_Page) is a rethinking of the storage stack, combining traditional file systems as well as volume managers into one cohesive tool. ZFS has some specific terminology that sets it apart from more traditional storage systems, however it has a great set of features with a focus on usability for systems administrators. ## ZFS Concepts ### Virtual Devices A VDEV (Virtual Device) in ZFS is analogous to a RAID device and similarly offers different benefits in terms of redundancy and performance. In general VDEV's offer better reliability and safety than a RAID card. It is discouraged to use a RAID setup with ZFS, as ZFS expects to directly manage the underlying disks. | VDEV Type | Similar RAID | Notes | |-----------|----------------|---------------------------------------| | Mirror | RAID 1 | Supports n-way mirroring for redundancy. | | raidz1 | RAID 5 | Single disk parity, offering fault tolerance of one disk failure. | | raidz2 | RAID 6 | Two-disk parity, can tolerate two disk failures. | | raidz3 | - | Three-disk parity, can tolerate three disk failures. | | Disk | - | Represents a single physical disk in a VDEV. | | File | - | File-based VDEV, not recommended for production as it adds complexity and reduces reliability. | Data in a ZFS storage pool is striped across all VDEVs. Adding more VDEVs, Logs, or Caches can increase IOPS (Input/Output Operations Per Second), enhancing performance. It's crucial to balance VDEVs for optimal performance and redundancy. ### Storage Pools ZFS uses Storage Pools as an abstraction over the lower level storage provider (VDEV), allow you to separate the user visible file system from the physical layout. ### ZFS Dataset ZFS datasets are analogous to traditional filesystems but with many more features. They provide many of ZFS's advantages. Datasets support [Copy on Write](https://en.wikipedia.org/wiki/Copy-on-write) snapshots, quota's, compression and de-duplication. ### Limits One directory may contain up to 2^48 files, up to 16 exabytes each. A single storage pool can contain up to 256 zettabytes (2^78) of space, and can be striped across 2^64 devices. A single host can have 2^64 storage pools. The limits are huge. ## Commands ### Storage Pools Actions: * List * Status * Destroy * Get/Set properties List zpools ```bash # Create a raidz zpool $ zpool create zroot raidz1 gpt/zfs0 gpt/zfs1 gpt/zfs2 # List ZPools $ zpool list NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT zroot 141G 106G 35.2G - 43% 75% 1.00x ONLINE - # List detailed information about a specific zpool $ zpool list -v zroot NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT zroot 141G 106G 35.2G - 43% 75% 1.00x ONLINE - gptid/c92a5ccf-a5bb-11e4-a77d-001b2172c655 141G 106G 35.2G - 43% 75% ``` Status of zpools ```bash # Get status information about zpools $ zpool status pool: zroot state: ONLINE scan: scrub repaired 0 in 2h51m with 0 errors on Thu Oct 1 07:08:31 2015 config: NAME STATE READ WRITE CKSUM zroot ONLINE 0 0 0 gptid/c92a5ccf-a5bb-11e4-a77d-001b2172c655 ONLINE 0 0 0 errors: No known data errors # Scrubbing a zpool to correct any errors $ zpool scrub zroot $ zpool status -v zroot pool: zroot state: ONLINE scan: scrub in progress since Thu Oct 15 16:59:14 2015 39.1M scanned out of 106G at 1.45M/s, 20h47m to go 0 repaired, 0.04% done config: NAME STATE READ WRITE CKSUM zroot ONLINE 0 0 0 gptid/c92a5ccf-a5bb-11e4-a77d-001b2172c655 ONLINE 0 0 0 errors: No known data errors ``` Properties of zpools ```bash # Getting properties from the pool properties can be user set or system provided. $ zpool get all zroot NAME PROPERTY VALUE SOURCE zroot size 141G - zroot capacity 75% - zroot altroot - default zroot health ONLINE - ... # Setting a zpool property $ zpool set comment="Storage of mah stuff" zroot $ zpool get comment NAME PROPERTY VALUE SOURCE tank comment - default zroot comment Storage of mah stuff local ``` Remove zpool ```bash $ zpool destroy test ``` ### Datasets Actions: * Create * List * Rename * Delete * Get/Set properties Create datasets ```bash # Create dataset $ zfs create zroot/root/data $ mount | grep data zroot/root/data on /data (zfs, local, nfsv4acls) # Create child dataset $ zfs create zroot/root/data/stuff $ mount | grep data zroot/root/data on /data (zfs, local, nfsv4acls) zroot/root/data/stuff on /data/stuff (zfs, local, nfsv4acls) # Create Volume $ zfs create -V zroot/win_vm $ zfs list zroot/win_vm NAME USED AVAIL REFER MOUNTPOINT zroot/win_vm 4.13G 17.9G 64K - ``` List datasets ```bash # List all datasets $ zfs list NAME USED AVAIL REFER MOUNTPOINT zroot 106G 30.8G 144K none zroot/ROOT 18.5G 30.8G 144K none zroot/ROOT/10.1 8K 30.8G 9.63G / zroot/ROOT/default 18.5G 30.8G 11.2G / zroot/backup 5.23G 30.8G 144K none zroot/home 288K 30.8G 144K none ... # List a specific dataset $ zfs list zroot/home NAME USED AVAIL REFER MOUNTPOINT zroot/home 288K 30.8G 144K none # List snapshots $ zfs list -t snapshot zroot@daily-2015-10-15 0 - 144K - zroot/ROOT@daily-2015-10-15 0 - 144K - zroot/ROOT/default@daily-2015-10-15 0 - 24.2G - zroot/tmp@daily-2015-10-15 124K - 708M - zroot/usr@daily-2015-10-15 0 - 144K - zroot/home@daily-2015-10-15 0 - 11.9G - zroot/var@daily-2015-10-15 704K - 1.42G - zroot/var/log@daily-2015-10-15 192K - 828K - zroot/var/tmp@daily-2015-10-15 0 - 152K - ``` Rename datasets ```bash $ zfs rename zroot/root/home zroot/root/old_home $ zfs rename zroot/root/new_home zroot/root/home ``` Delete dataset ```bash # Datasets cannot be deleted if they have any snapshots $ zfs destroy zroot/root/home ``` Get / set properties of a dataset ```bash # Get all properties $ zfs get all zroot/usr/home NAME PROPERTY VALUE SOURCE zroot/home type filesystem - zroot/home creation Mon Oct 20 14:44 2014 - zroot/home used 11.9G - zroot/home available 94.1G - zroot/home referenced 11.9G - zroot/home mounted yes - ... # Get property from dataset $ zfs get compression zroot/usr/home NAME PROPERTY VALUE SOURCE zroot/home compression off default # Set property on dataset $ zfs set compression=lz4 zroot/lamb # Get a set of properties from all datasets $ zfs list -o name,quota,reservation NAME QUOTA RESERV zroot none none zroot/ROOT none none zroot/ROOT/default none none zroot/tmp none none zroot/usr none none zroot/home none none zroot/var none none ... ``` ### Write Log Pool The ZFS Intent Log (ZIL) is a write log designed to speed up synchronous writes. This is typically a faster drive or drive partition than the larger storage pools. ```bash # Add a log pool $ zpool add mypool/lamb log /dev/sdX # Check the configuration $ zpool status mypool/lamb ``` ### Read Cache Pool The Level 2 Adaptive Replacement Cache (L2ARC) extends the primary ARC (in-RAM cache) and is used for read caching. This is typically a faster drive or drive partition than the larger storage pools. ```bash # Add a cache pool $ zpool add mypool/lamb cache /dev/sdY # Check the configuration $ zpool status mypool/lamb ``` ### Data Compression Data compression reduces the amount of space data occupies on disk in exchange for some extra CPU usage. When enabled, it can enhance performance by reducing the amount of disk I/O. It especially beneficial on systems with more CPU resources than disk bandwidth. ```bash # Get compression options $ zfs get -help ... compression NO YES on | off | lzjb | gzip | gzip-[1-9] | zle | lz4 | zstd | zstd-[1-19] | zstd-fast | zstd-fast-[1-10,20,30,40,50,60,70,80,90,100,500,1000] ... # Set compression $ zfs set compression=on mypool/lamb # Check the configuration $ zpool get compression mypool/lamb ``` ### Encryption at Rest Encryption allows data to be encrypted on the device at the cost of extra CPU cycles. This property can only be set when a dataset is being created. ```bash # Enable encryption on the pool $ zpool set feature@encryption=enabled black_hole # Create an encrypted dataset with a prompt $ zfs create -o encryption=on -o keyformat=passphrase black_hole/enc # Check the configuration $ zfs get encryption black_hole/enc ``` It should be noted that there are parts of the system where the data is not encrypted. See the table below for a breakdown. | Component | Encrypted | Notes | |----------------------|-------------------------------------------|------------------------------------------------------| | Main Data Storage | Yes | Data in datasets/volumes is encrypted. | | ZFS Intent Log (ZIL) | Yes | Synchronous write requests are encrypted. | | L2ARC (Cache) | Yes | Cached data is stored in an encrypted form. | | RAM (ARC) | No | Data in the primary ARC, in RAM, is not encrypted. | | Swap Area | Conditional | Encrypted if the ZFS swap dataset is encrypted. | | ZFS Metadata | Yes | Metadata is encrypted for encrypted datasets. | | Snapshot Data | Yes | Snapshots of encrypted datasets are also encrypted. | | ZFS Send/Receive | Conditional | Encrypted during send/receive if datasets are encrypted and `-w` flag is used. | ### Snapshots ZFS snapshots are one of the things about zfs that are a really big deal * The space they take up is equal to the difference in data between the filesystem and its snapshot * Creation time is only seconds * Recovery is as fast as you can write data. * They are easy to automate. Actions: * Create * Delete * Rename * Access snapshots * Send / Receive * Clone Create snapshots ```bash # Create a snapshot of a single dataset zfs snapshot zroot/home/sarlalian@now # Create a snapshot of a dataset and its children $ zfs snapshot -r zroot/home@now $ zfs list -t snapshot NAME USED AVAIL REFER MOUNTPOINT zroot/home@now 0 - 26K - zroot/home/sarlalian@now 0 - 259M - zroot/home/alice@now 0 - 156M - zroot/home/bob@now 0 - 156M - ... ``` Destroy snapshots ```bash # How to destroy a snapshot $ zfs destroy zroot/home/sarlalian@now # Delete a snapshot on a parent dataset and its children $ zfs destroy -r zroot/home/sarlalian@now ``` Renaming Snapshots ```bash # Rename a snapshot $ zfs rename zroot/home/sarlalian@now zroot/home/sarlalian@today $ zfs rename zroot/home/sarlalian@now today $ zfs rename -r zroot/home@now @yesterday ``` Accessing snapshots ```bash # CD into a snapshot directory $ cd /home/.zfs/snapshot/ ``` Sending and Receiving ```bash # Backup a snapshot to a file $ zfs send zroot/home/sarlalian@now | gzip > backup_file.gz # Send a snapshot to another dataset $ zfs send zroot/home/sarlalian@now | zfs recv backups/home/sarlalian # Send a snapshot to a remote host $ zfs send zroot/home/sarlalian@now | ssh root@backup_server 'zfs recv zroot/home/sarlalian' # Send full dataset with snapshots to new host $ zfs send -v -R zroot/home@now | ssh root@backup_server 'zfs recv zroot/home' ``` Cloning Snapshots ```bash # Clone a snapshot $ zfs clone zroot/home/sarlalian@now zroot/home/sarlalian_new # Promoting the clone so it is no longer dependent on the snapshot $ zfs promote zroot/home/sarlalian_new ``` ### Putting it all together This following a script utilizing FreeBSD, jails and ZFS to automate provisioning a clean copy of a MySQL staging database from a live replication slave. ```bash #!/bin/sh echo "==== Stopping the staging database server ====" jail -r staging echo "==== Cleaning up existing staging server and snapshot ====" zfs destroy -r zroot/jails/staging zfs destroy zroot/jails/slave@staging echo "==== Quiescing the slave database ====" echo "FLUSH TABLES WITH READ LOCK;" | /usr/local/bin/mysql -u root -pmyrootpassword -h slave echo "==== Snapshotting the slave db filesystem as zroot/jails/slave@staging ====" zfs snapshot zroot/jails/slave@staging echo "==== Starting the slave database server ====" jail -c slave echo "==== Cloning the slave snapshot to the staging server ====" zfs clone zroot/jails/slave@staging zroot/jails/staging echo "==== Installing the staging mysql config ====" mv /jails/staging/usr/local/etc/my.cnf /jails/staging/usr/local/etc/my.cnf.slave cp /jails/staging/usr/local/etc/my.cnf.staging /jails/staging/usr/local/etc/my.cnf echo "==== Setting up the staging rc.conf file ====" mv /jails/staging/etc/rc.conf.local /jails/staging/etc/rc.conf.slave mv /jails/staging/etc/rc.conf.staging /jails/staging/etc/rc.conf.local echo "==== Starting the staging db server ====" jail -c staging echo "==== Makes the staging database not pull from the master ====" echo "STOP SLAVE;" | /usr/local/bin/mysql -u root -pmyrootpassword -h staging echo "RESET SLAVE;" | /usr/local/bin/mysql -u root -pmyrootpassword -h staging ``` ### Additional Reading * [BSDNow's Crash Course on ZFS](http://www.bsdnow.tv/tutorials/zfs) * [FreeBSD Handbook on ZFS](https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/zfs.html) * [BSDNow's Crash Course on ZFS](http://www.bsdnow.tv/tutorials/zfs) * [Oracle's Tuning Guide](http://www.oracle.com/technetwork/articles/servers-storage-admin/sto-recommended-zfs-settings-1951715.html) * [OpenZFS Tuning Guide](http://open-zfs.org/wiki/Performance_tuning) * [FreeBSD ZFS Tuning Guide](https://wiki.freebsd.org/ZFSTuningGuide)