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---
category: tool
tool: zfs
contributors:
- ["sarlalian", "http://github.com/sarlalian"]
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 is similar to a raid device presented by a RAID card, there are several different
types of VDEV's that offer various advantages, including redundancy and speed. 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.
Types of VDEV's
* stripe (a single disk, no redundancy)
* mirror (n-way mirrors supported)
* raidz
* raidz1 (1-disk parity, similar to RAID 5)
* raidz2 (2-disk parity, similar to RAID 6)
* raidz3 (3-disk parity, no RAID analog)
* disk
* file (not recommended for production due to another filesystem adding unnecessary layering)
Your data is striped across all the VDEV's present in your Storage Pool, so more VDEV's will
increase your IOPS.
### 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 bucket 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 tank/root/data
$ mount | grep data
tank/root/data on /data (zfs, local, nfsv4acls)
# Create child dataset
$ zfs create tank/root/data/stuff
$ mount | grep data
tank/root/data on /data (zfs, local, nfsv4acls)
tank/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
tank/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 tank/root/home tank/root/old_home
$ zfs rename tank/root/new_home tank/root/home
```
Delete dataset
```bash
# Datasets cannot be deleted if they have any snapshots
$ zfs destroy tank/root/home
```
Get / set properties of a dataset
```bash
# Get all properties
$ zfs get all zroot/usr/home │157 # Create Volume
NAME PROPERTY VALUE SOURCE │158 $ zfs create -V zroot/win_vm
zroot/home type filesystem - │159 $ zfs list zroot/win_vm
zroot/home creation Mon Oct 20 14:44 2014 - │160 NAME USED AVAIL REFER MOUNTPOINT
zroot/home used 11.9G - │161 tank/win_vm 4.13G 17.9G 64K -
zroot/home available 94.1G - │162 ```
zroot/home referenced 11.9G - │163
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=gzip-9 mypool/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
...
```
### 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 tank/home/sarlalian@now
# Create a snapshot of a dataset and its children
$ zfs snapshot -r tank/home@now
$ zfs list -t snapshot
NAME USED AVAIL REFER MOUNTPOINT
tank/home@now 0 - 26K -
tank/home/sarlalian@now 0 - 259M -
tank/home/alice@now 0 - 156M -
tank/home/bob@now 0 - 156M -
...
```
Destroy snapshots
```bash
# How to destroy a snapshot
$ zfs destroy tank/home/sarlalian@now
# Delete a snapshot on a parent dataset and its children
$ zfs destroy -r tank/home/sarlalian@now
```
Renaming Snapshots
```bash
# Rename a snapshot
$ zfs rename tank/home/sarlalian@now tank/home/sarlalian@today
$ zfs rename tank/home/sarlalian@now today
$ zfs rename -r tank/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 tank/home/sarlalian@now | gzip > backup_file.gz
# Send a snapshot to another dataset
$ zfs send tank/home/sarlalian@now | zfs recv backups/home/sarlalian
# Send a snapshot to a remote host
$ zfs send tank/home/sarlalian@now | ssh root@backup_server 'zfs recv tank/home/sarlalian'
# Send full dataset with snapshots to new host
$ zfs send -v -R tank/home@now | ssh root@backup_server 'zfs recv tank/home'
```
Cloning Snapshots
```bash
# Clone a snapshot
$ zfs clone tank/home/sarlalian@now tank/home/sarlalian_new
# Promoting the clone so it is no longer dependent on the snapshot
$ zfs promote tank/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)
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