Basics

The Basics

Let’s create a pool and mount a file system.

Create a Pool

A ‘pool’ is group of disks and that’s where RAID levels are established. You can choose to mirror drives, or use distributed parity. A common choice is RAIDZ1 so that you can sustain the loss of one drive. You can increase the redundancy to RAIDZ2 and RAIDZ3 as desired.

zpool create pool01 raidz1 /dev/sdc /dev/sdd /dev/sde /dev/sdf

zpool list
NAME               SIZE  ALLOC   FREE  
pool01              40T     0T    40T 

Create a Filesystem

A default root file system is created and mounted automatically when the pool is created. Using this is fine and you can easily change where it’s mounted.

zfs list

NAME     USED  AVAIL     REFER  MOUNTPOINT
pool01     0T    40T        0T  /pool01

zfs set mountpoint=/mnt pool01

But often, you need more than one file system - say one for holding working files and another for long term storage. This allows you to easily back up things different things, differently.

# Get rid of the initial fs and pool
zpool destroy pool01

# Create it again but leave the root filesystem unmounted with the `-m` option. You can also use drive short-names
zpool create -m none pool01 raidz1 sdc sdd sde sdf

# Add a couple filesystems and mount under the /srv directory
zfs create pool01/working -o  mountpoint=/srv/working
zfs create pool01/archive -o  mountpoint=/srv/archive             
              ^     ^
             /       \
pool name --          filesystem name

Now you can do things like snapshot the archive folder regularly while skipping the working folder. The only downside is that they are separate filessytems. Moving things doesn’t happen instantly.

Compression

Compression is on by default and this will save space for things that can benefit from it. It also makes things faster as moving compressed data takes less time. CPU use for the default algorithm lz4, is negligible and it quickly detects files that aren’t compressible and gives up so that CPU time isn’t wasted.

zfs get compression pool01

NAME    PROPERTY     VALUE           SOURCE
pool01  compression  lz4             local

Next Step

Now you’ve got a filesystem, take a look at creating and work with snapshots.