ZFS on Linux
------------
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ZFS is a combined file system and logical volume manager designed by
Sun Microsystems. Starting with {pve} 3.4, the native Linux
kernel port of the ZFS file system is introduced as optional
file system and also as an additional selection for the root
file system. There is no need for manually compile ZFS modules - all
packages are included.

By using ZFS, its possible to achieve maximum enterprise features with
low budget hardware, but also high performance systems by leveraging
SSD caching or even SSD only setups. ZFS can replace cost intense
hardware raid cards by moderate CPU and memory load combined with easy
management.

.General ZFS advantages

* Easy configuration and management with {pve} GUI and CLI.

* Reliable

* Protection against data corruption

* Data compression on file system level

* Snapshots

* Copy-on-write clone

* Various raid levels: RAID0, RAID1, RAID10, RAIDZ-1, RAIDZ-2 and RAIDZ-3

* Can use SSD for cache

* Self healing

* Continuous integrity checking

* Designed for high storage capacities

* Protection against data corruption

* Asynchronous replication over network

* Open Source

* Encryption

* ...


Hardware
~~~~~~~~

ZFS depends heavily on memory, so you need at least 8GB to start. In
practice, use as much you can get for your hardware/budget. To prevent
data corruption, we recommend the use of high quality ECC RAM.

If you use a dedicated cache and/or log disk, you should use a
enterprise class SSD (e.g. Intel SSD DC S3700 Series). This can
increase the overall performance significantly.

IMPORTANT: Do not use ZFS on top of hardware controller which has its
own cache management. ZFS needs to directly communicate with disks. An
HBA adapter is the way to go, or something like LSI controller flashed
in ``IT'' mode.

If you are experimenting with an installation of {pve} inside a VM
(Nested Virtualization), don't use `virtio` for disks of that VM,
since they are not supported by ZFS. Use IDE or SCSI instead (works
also with `virtio` SCSI controller type).


Installation as Root File System
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When you install using the {pve} installer, you can choose ZFS for the
root file system. You need to select the RAID type at installation
time:

[horizontal]
RAID0:: Also called ``striping''. The capacity of such volume is the sum
of the capacities of all disks. But RAID0 does not add any redundancy,
so the failure of a single drive makes the volume unusable.

RAID1:: Also called ``mirroring''. Data is written identically to all
disks. This mode requires at least 2 disks with the same size. The
resulting capacity is that of a single disk.

RAID10:: A combination of RAID0 and RAID1. Requires at least 4 disks.

RAIDZ-1:: A variation on RAID-5, single parity. Requires at least 3 disks.

RAIDZ-2:: A variation on RAID-5, double parity. Requires at least 4 disks.

RAIDZ-3:: A variation on RAID-5, triple parity. Requires at least 5 disks.

The installer automatically partitions the disks, creates a ZFS pool
called `rpool`, and installs the root file system on the ZFS subvolume
`rpool/ROOT/pve-1`.

Another subvolume called `rpool/data` is created to store VM
images. In order to use that with the {pve} tools, the installer
creates the following configuration entry in `/etc/pve/storage.cfg`:

----
zfspool: local-zfs
	pool rpool/data
	sparse
	content images,rootdir
----

After installation, you can view your ZFS pool status using the
`zpool` command:

----
# zpool status
  pool: rpool
 state: ONLINE
  scan: none requested
config:

	NAME        STATE     READ WRITE CKSUM
	rpool       ONLINE       0     0     0
	  mirror-0  ONLINE       0     0     0
	    sda2    ONLINE       0     0     0
	    sdb2    ONLINE       0     0     0
	  mirror-1  ONLINE       0     0     0
	    sdc     ONLINE       0     0     0
	    sdd     ONLINE       0     0     0

errors: No known data errors
----

The `zfs` command is used configure and manage your ZFS file
systems. The following command lists all file systems after
installation:

----
# zfs list
NAME               USED  AVAIL  REFER  MOUNTPOINT
rpool             4.94G  7.68T    96K  /rpool
rpool/ROOT         702M  7.68T    96K  /rpool/ROOT
rpool/ROOT/pve-1   702M  7.68T   702M  /
rpool/data          96K  7.68T    96K  /rpool/data
rpool/swap        4.25G  7.69T    64K  -
----


Bootloader
~~~~~~~~~~

The default ZFS disk partitioning scheme does not use the first 2048
sectors. This gives enough room to install a GRUB boot partition. The
{pve} installer automatically allocates that space, and installs the
GRUB boot loader there. If you use a redundant RAID setup, it installs
the boot loader on all disk required for booting. So you can boot
even if some disks fail.

NOTE: It is not possible to use ZFS as root file system with UEFI
boot.


ZFS Administration
~~~~~~~~~~~~~~~~~~

This section gives you some usage examples for common tasks. ZFS
itself is really powerful and provides many options. The main commands
to manage ZFS are `zfs` and `zpool`. Both commands come with great
manual pages, which can be read with:

----
# man zpool
# man zfs
-----

.Create a new zpool

To create a new pool, at least one disk is needed. The `ashift` should
have the same sector-size (2 power of `ashift`) or larger as the
underlying disk.

 zpool create -f -o ashift=12 <pool> <device>

To activate compression

 zfs set compression=lz4 <pool>

.Create a new pool with RAID-0

Minimum 1 Disk

 zpool create -f -o ashift=12 <pool> <device1> <device2>

.Create a new pool with RAID-1

Minimum 2 Disks

 zpool create -f -o ashift=12 <pool> mirror <device1> <device2>

.Create a new pool with RAID-10

Minimum 4 Disks

 zpool create -f -o ashift=12 <pool> mirror <device1> <device2> mirror <device3> <device4> 

.Create a new pool with RAIDZ-1

Minimum 3 Disks

 zpool create -f -o ashift=12 <pool> raidz1 <device1> <device2> <device3>

.Create a new pool with RAIDZ-2

Minimum 4 Disks

 zpool create -f -o ashift=12 <pool> raidz2 <device1> <device2> <device3> <device4>

.Create a new pool with cache (L2ARC)

It is possible to use a dedicated cache drive partition to increase
the performance (use SSD).

As `<device>` it is possible to use more devices, like it's shown in
"Create a new pool with RAID*".

 zpool create -f -o ashift=12 <pool> <device> cache <cache_device>

.Create a new pool with log (ZIL)

It is possible to use a dedicated cache drive partition to increase
the performance(SSD).

As `<device>` it is possible to use more devices, like it's shown in
"Create a new pool with RAID*".

 zpool create -f -o ashift=12 <pool> <device> log <log_device>

.Add cache and log to an existing pool

If you have an pool without cache and log. First partition the SSD in
2 partition with `parted` or `gdisk`

IMPORTANT: Always use GPT partition tables.

The maximum size of a log device should be about half the size of
physical memory, so this is usually quite small. The rest of the SSD
can be used as cache.

 zpool add -f <pool> log <device-part1> cache <device-part2> 

.Changing a failed device

 zpool replace -f <pool> <old device> <new-device>


Activate E-Mail Notification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ZFS comes with an event daemon, which monitors events generated by the
ZFS kernel module. The daemon can also send emails on ZFS events like
pool errors. Newer ZFS packages ships the daemon in a sparate package,
and you can install it using `apt-get`:

----
# apt-get install zfs-zed
----

To activate the daemon it is necessary to edit `/etc/zfs/zed.d/zed.rc` with your
favourite editor, and uncomment the `ZED_EMAIL_ADDR` setting:

--------
ZED_EMAIL_ADDR="root"
--------

Please note {pve} forwards mails to `root` to the email address
configured for the root user.

IMPORTANT: The only setting that is required is `ZED_EMAIL_ADDR`. All
other settings are optional.


Limit ZFS Memory Usage
~~~~~~~~~~~~~~~~~~~~~~

It is good to use at most 50 percent (which is the default) of the
system memory for ZFS ARC to prevent performance shortage of the
host. Use your preferred editor to change the configuration in
`/etc/modprobe.d/zfs.conf` and insert:

--------
options zfs zfs_arc_max=8589934592
--------

This example setting limits the usage to 8GB.

[IMPORTANT]
====
If your root file system is ZFS you must update your initramfs every
time this value changes:

 update-initramfs -u
====


.SWAP on ZFS

SWAP on ZFS on Linux may generate some troubles, like blocking the
server or generating a high IO load, often seen when starting a Backup
to an external Storage.

We strongly recommend to use enough memory, so that you normally do not
run into low memory situations. Additionally, you can lower the
``swappiness'' value. A good value for servers is 10:

 sysctl -w vm.swappiness=10

To make the swappiness persistent, open `/etc/sysctl.conf` with
an editor of your choice and add the following line:

--------
vm.swappiness = 10
--------

.Linux kernel `swappiness` parameter values
[width="100%",cols="<m,2d",options="header"]
|===========================================================
| Value               | Strategy
| vm.swappiness = 0   | The kernel will swap only to avoid
an 'out of memory' condition
| vm.swappiness = 1   | Minimum amount of swapping without
disabling it entirely.
| vm.swappiness = 10  | This value is sometimes recommended to
improve performance when sufficient memory exists in a system.
| vm.swappiness = 60  | The default value.
| vm.swappiness = 100 | The kernel will swap aggressively.
|===========================================================
