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ZFS is a combined file system and logical volume manager designed bySun Microsystems. Starting with Proxmox VE 3.4, the native Linuxkernel port of the ZFS file system is introduced as optionalfile system and also as an additional selection for the rootfile system. There is no need for manually compile ZFS modules - allpackages are included.
By using ZFS, its possible to achieve maximum enterprise features withlow budget hardware, but also high performance systems by leveragingSSD caching or even SSD only setups. ZFS can replace cost intensehardware raid cards by moderate CPU and memory load combined with easymanagement.
General ZFS advantages
Easy configuration and management with Proxmox VE 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, RAIDZ-3,dRAID, dRAID2, dRAID3
Can use SSD for cache
Self healing
Continuous integrity checking
Designed for high storage capacities
Asynchronous replication over network
Open Source
Encryption
…
Hardware
ZFS depends heavily on memory, so you need at least 8GB to start. Inpractice, use as much as you can get for your hardware/budget. To preventdata corruption, we recommend the use of high quality ECC RAM.
If you use a dedicated cache and/or log disk, you should use anenterprise class SSD. This canincrease the overall performance significantly.
 | Do not use ZFS on top of a hardware RAID controller which has itsown cache management. ZFS needs to communicate directly with the disks. AnHBA adapter or something like an LSI controller flashed in “IT” mode is moreappropriate. |
If you are experimenting with an installation of Proxmox VE inside a VM(Nested Virtualization), don’t use virtio for disks of that VM,as they are not supported by ZFS. Use IDE or SCSI instead (also workswith the virtio SCSI controller type).
Installation as Root File System
When you install using the Proxmox VE installer, you can choose ZFS for theroot file system. You need to select the RAID type at installationtime:
| RAID0 | Also called “striping”. The capacity of such volume is the sumof 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 alldisks. This mode requires at least 2 disks with the same size. Theresulting 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 poolcalled rpool, and installs the root file system on the ZFS subvolumerpool/ROOT/pve-1.
Another subvolume called rpool/data is created to store VMimages. In order to use that with the Proxmox VE tools, the installercreates 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 thezpool command:
# zpool status pool: rpool state: ONLINE scan: none requestedconfig: 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 0errors: No known data errors
The zfs command is used to configure and manage your ZFS file systems. Thefollowing command lists all file systems after installation:
# zfs listNAME USED AVAIL REFER MOUNTPOINTrpool 4.94G 7.68T 96K /rpoolrpool/ROOT 702M 7.68T 96K /rpool/ROOTrpool/ROOT/pve-1 702M 7.68T 702M /rpool/data 96K 7.68T 96K /rpool/datarpool/swap 4.25G 7.69T 64K -
ZFS RAID Level Considerations
There are a few factors to take into consideration when choosing the layout ofa ZFS pool. The basic building block of a ZFS pool is the virtual device, orvdev. All vdevs in a pool are used equally and the data is striped among them(RAID0). Check the zpoolconcepts(7) manpage for more details on vdevs.
Performance
Each vdev type has different performance behaviors. The twoparameters of interest are the IOPS (Input/Output Operations per Second) andthe bandwidth with which data can be written or read.
A mirror vdev (RAID1) will approximately behave like a single disk in regardto both parameters when writing data. When reading data the performance willscale linearly with the number of disks in the mirror.
A common situation is to have 4 disks. When setting it up as 2 mirror vdevs(RAID10) the pool will have the write characteristics as two single disks inregard to IOPS and bandwidth. For read operations it will resemble 4 singledisks.
A RAIDZ of any redundancy level will approximately behave like a single diskin regard to IOPS with a lot of bandwidth. How much bandwidth depends on thesize of the RAIDZ vdev and the redundancy level.
A dRAID pool should match the performance of an equivalent RAIDZ pool.
For running VMs, IOPS is the more important metric in most situations.
Size, Space usage and Redundancy
While a pool made of mirror vdevs will have the best performancecharacteristics, the usable space will be 50% of the disks available. Less if amirror vdev consists of more than 2 disks, for example in a 3-way mirror. Atleast one healthy disk per mirror is needed for the pool to stay functional.
The usable space of a RAIDZ type vdev of N disks is roughly N-P, with P beingthe RAIDZ-level. The RAIDZ-level indicates how many arbitrary disks can failwithout losing data. A special case is a 4 disk pool with RAIDZ2. In thissituation it is usually better to use 2 mirror vdevs for the better performanceas the usable space will be the same.
Another important factor when using any RAIDZ level is how ZVOL datasets, whichare used for VM disks, behave. For each data block the pool needs parity datawhich is at least the size of the minimum block size defined by the ashiftvalue of the pool. With an ashift of 12 the block size of the pool is 4k. Thedefault block size for a ZVOL is 8k. Therefore, in a RAIDZ2 each 8k blockwritten will cause two additional 4k parity blocks to be written,8k + 4k + 4k = 16k. This is of course a simplified approach and the realsituation will be slightly different with metadata, compression and such notbeing accounted for in this example.
This behavior can be observed when checking the following properties of theZVOL:
volsize
refreservation (if the pool is not thin provisioned)
used (if the pool is thin provisioned and without snapshots present)
# zfs get volsize,refreservation,used <pool>/vm-<vmid>-disk-X
volsize is the size of the disk as it is presented to the VM, whilerefreservation shows the reserved space on the pool which includes theexpected space needed for the parity data. If the pool is thin provisioned, therefreservation will be set to 0. Another way to observe the behavior is tocompare the used disk space within the VM and the used property. Be awarethat snapshots will skew the value.
There are a few options to counter the increased use of space:
Increase the volblocksize to improve the data to parity ratio
Use mirror vdevs instead of RAIDZ
Use ashift=9 (block size of 512 bytes)
The volblocksize property can only be set when creating a ZVOL. The defaultvalue can be changed in the storage configuration. When doing this, the guestneeds to be tuned accordingly and depending on the use case, the problem ofwrite amplification is just moved from the ZFS layer up to the guest.
Using ashift=9 when creating the pool can lead to badperformance, depending on the disks underneath, and cannot be changed later on.
Mirror vdevs (RAID1, RAID10) have favorable behavior for VM workloads. Usethem, unless your environment has specific needs and characteristics whereRAIDZ performance characteristics are acceptable.
ZFS dRAID
In a ZFS dRAID (declustered RAID) the hot spare drive(s) participate in the RAID.Their spare capacity is reserved and used for rebuilding when one drive fails.This provides, depending on the configuration, faster rebuilding compared to aRAIDZ in case of drive failure. More information can be found in the officialOpenZFS documentation.
[OpenZFS dRAIDhttps://openzfs.github.io/openzfs-docs/Basic%20Concepts/dRAID%20Howto.html]
| dRAID is intended for more than 10-15 disks in a dRAID. A RAIDZsetup should be better for a lower amount of disks in most use cases. |
| The GUI requires one more disk than the minimum (i.e. dRAID1 needs 3). Itexpects that a spare disk is added as well. |
dRAID1 or dRAID: requires at least 2 disks, one can fail before data islost
dRAID2: requires at least 3 disks, two can fail before data is lost
dRAID3: requires at least 4 disks, three can fail before data is lost
Additional information can be found on the manual page:
# man zpoolconcepts
Spares and Data
The number of spares tells the system how many disks it should keep ready incase of a disk failure. The default value is 0 spares. Without spares,rebuilding won’t get any speed benefits.
data defines the number of devices in a redundancy group. The default value is8. Except when disks - parity - spares equal something less than 8, the lowernumber is used. In general, a smaller number of data devices leads to higherIOPS, better compression ratios and faster resilvering, but defining fewer datadevices reduces the available storage capacity of the pool.
Bootloader
Proxmox VE uses proxmox-boot-tool to manage thebootloader configuration.See the chapter on Proxmox VE host bootloaders for details.
ZFS Administration
This section gives you some usage examples for common tasks. ZFSitself is really powerful and provides many options. The main commandsto manage ZFS are zfs and zpool. Both commands come with greatmanual 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 thesame sector-size (2 power of ashift) or larger as the underlying disk.
# zpool create -f -o ashift=12 <pool> <device>
| Pool names must adhere to the following rules:
|
To activate compression (see section Compression in ZFS):
# 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>
Please read the section forZFS RAID Level Considerationsto get a rough estimate on how IOPS and bandwidth expectations before setting upa pool, especially when wanting to use a RAID-Z mode.
Create a new pool with cache (L2ARC)
It is possible to use a dedicated device, or partition, as second-level cache toincrease the performance. Such a cache device will especially help withrandom-read workloads of data that is mostly static. As it acts as additionalcaching layer between the actual storage, and the in-memory ARC, it can alsohelp if the ARC must be reduced due to memory constraints.
Create ZFS pool with a on-disk cache
# zpool create -f -o ashift=12 <pool> <device> cache <cache-device>
Here only a single <device> and a single <cache-device> was used, but it ispossible to use more devices, like it’s shown inCreate a new pool with RAID.
Note that for cache devices no mirror or raid modi exist, they are all simplyaccumulated.
If any cache device produces errors on read, ZFS will transparently divert thatrequest to the underlying storage layer.
Create a new pool with log (ZIL)
It is possible to use a dedicated drive, or partition, for the ZFS Intent Log(ZIL), it is mainly used to provide safe synchronous transactions, so often inperformance critical paths like databases, or other programs that issue fsyncoperations more frequently.
The pool is used as default ZIL location, diverting the ZIL IO load to aseparate device can, help to reduce transaction latencies while relieving themain pool at the same time, increasing overall performance.
For disks to be used as log devices, directly or through a partition, it’srecommend to:
use fast SSDs with power-loss protection, as those have much smaller commit latencies.
Use at least a few GB for the partition (or whole device), but using more than half of your installed memory won’t provide you with any real advantage.
Create ZFS pool with separate log device
# zpool create -f -o ashift=12 <pool> <device> log <log-device>
In above example a single <device> and a single <log-device> is used, but youcan also combine this with other RAID variants, as described in theCreate a new pool with RAID section.
You can also mirror the log device to multiple devices, this is mainly useful toensure that performance doesn’t immediately degrades if a single log devicefails.
If all log devices fail the ZFS main pool itself will be used again, until thelog device(s) get replaced.
Add cache and log to an existing pool
If you have a pool without cache and log you can still add both, or just one ofthem, at any time.
For example, let’s assume you got a good enterprise SSD with power-lossprotection that you want to use for improving the overall performance of yourpool.
As the maximum size of a log device should be about half the size of theinstalled physical memory, it means that the ZIL will mostly likely only take upa relatively small part of the SSD, the remaining space can be used as cache.
First you have to create two GPT partitions on the SSD with parted or gdisk.
Then you’re ready to add them to an pool:
Add both, a separate log device and a second-level cache, to an existing pool
# zpool add -f <pool> log <device-part1> cache <device-part2>
Just replay <pool>, <device-part1> and <device-part2> with the pool nameand the two /dev/disk/by-id/ paths to the partitions.
You can also add ZIL and cache separately.
Add a log device to an existing ZFS pool
# zpool add <pool> log <log-device>
Changing a failed device
# zpool replace -f <pool> <old-device> <new-device>
Changing a failed bootable device
Depending on how Proxmox VE was installed it is either using systemd-boot or GRUBthrough proxmox-boot-tool
[Systems installed with Proxmox VE 6.4 or later,EFI systems installed with Proxmox VE 5.4 or later]
or plain GRUB as bootloader (seeHost Bootloader). You can check by running:
# proxmox-boot-tool status
The first steps of copying the partition table, reissuing GUIDs and replacingthe ZFS partition are the same. To make the system bootable from the new disk,different steps are needed which depend on the bootloader in use.
# sgdisk <healthy bootable device> -R <new device># sgdisk -G <new device># zpool replace -f <pool> <old zfs partition> <new zfs partition>
| Use the zpool status -v command to monitor how far the resilveringprocess of the new disk has progressed. |
With
proxmox-boot-tool:
# proxmox-boot-tool format <new disk's ESP># proxmox-boot-tool init <new disk's ESP> [grub]
| ESP stands for EFI System Partition, which is setup as partition #2 onbootable disks setup by the Proxmox VE installer since version 5.4. For details, seeSetting up a new partition for use as synced ESP. |
| Make sure to pass grub as mode to proxmox-boot-tool init ifproxmox-boot-tool status indicates your current disks are using GRUB,especially if Secure Boot is enabled! |
With plain GRUB:
# grub-install <new disk>
| Plain GRUB is only used on systems installed with Proxmox VE 6.3 or earlier,which have not been manually migrated to using proxmox-boot-tool yet. |
Configure E-Mail Notification
ZFS comes with an event daemon ZED, which monitors events generated by the ZFSkernel module. The daemon can also send emails on ZFS events like pool errors.Newer ZFS packages ship the daemon in a separate zfs-zed package, which shouldalready be installed by default in Proxmox VE.
You can configure the daemon via the file /etc/zfs/zed.d/zed.rc with yourfavorite editor. The required setting for email notification isZED_EMAIL_ADDR, which is set to root by default.
ZED_EMAIL_ADDR="root"
Please note Proxmox VE forwards mails to root to the email addressconfigured for the root user.
Limit ZFS Memory Usage
ZFS uses 50 % of the host memory for the Adaptive ReplacementCache (ARC) by default. For new installations starting with Proxmox VE 8.1, theARC usage limit will be set to 10 % of the installed physical memory, clampedto a maximum of 16 GiB. This value is written to /etc/modprobe.d/zfs.conf.
Allocating enough memory for the ARC is crucial for IO performance, so reduce itwith caution. As a general rule of thumb, allocate at least 2 GiB Base + 1GiB/TiB-Storage. For example, if you have a pool with 8 TiB of availablestorage space then you should use 10 GiB of memory for the ARC.
ZFS also enforces a minimum value of 64 MiB.
You can change the ARC usage limit for the current boot (a reboot resets thischange again) by writing to the zfs_arc_max module parameter directly:
echo "$[10 * 1024*1024*1024]" >/sys/module/zfs/parameters/zfs_arc_max
To permanently change the ARC limits, add (or change if already present) thefollowing line to /etc/modprobe.d/zfs.conf:
options zfs zfs_arc_max=8589934592
This example setting limits the usage to 8 GiB (8 * 230).
| In case your desired zfs_arc_max value is lower than or equal tozfs_arc_min (which defaults to 1/32 of the system memory), zfs_arc_max willbe ignored unless you also set zfs_arc_min to at most zfs_arc_max - 1. |
echo "$[8 * 1024*1024*1024 - 1]" >/sys/module/zfs/parameters/zfs_arc_minecho "$[8 * 1024*1024*1024]" >/sys/module/zfs/parameters/zfs_arc_max
This example setting (temporarily) limits the usage to 8 GiB (8 * 230) onsystems with more than 256 GiB of total memory, where simply settingzfs_arc_max alone would not work.
| If your root file system is ZFS, you must update your initramfs everytime this value changes: # update-initramfs -u -k all You must reboot to activate these changes. |
SWAP on ZFS
Swap-space created on a zvol may generate some troubles, like blocking theserver or generating a high IO load, often seen when starting a Backupto an external Storage.
We strongly recommend to use enough memory, so that you normally do notrun into low memory situations. Should you need or want to add swap, it ispreferred to create a partition on a physical disk and use it as a swap device.You can leave some space free for this purpose in the advanced options of theinstaller. 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 withan editor of your choice and add the following line:
vm.swappiness = 10
| Value | Strategy |
|---|---|
vm.swappiness = 0 | The kernel will swap only to avoidan out of memory condition |
vm.swappiness = 1 | Minimum amount of swapping withoutdisabling it entirely. |
vm.swappiness = 10 | This value is sometimes recommended toimprove performance when sufficient memory exists in a system. |
vm.swappiness = 60 | The default value. |
vm.swappiness = 100 | The kernel will swap aggressively. |
Encrypted ZFS Datasets
| Native ZFS encryption in Proxmox VE is experimental. Known limitations andissues include Replication with encrypted datasets [https://bugzilla.proxmox.com/show_bug.cgi?id=2350] ,as well as checksum errors when using Snapshots or ZVOLs. [https://github.com/openzfs/zfs/issues/11688] |
ZFS on Linux version 0.8.0 introduced support for native encryption ofdatasets. After an upgrade from previous ZFS on Linux versions, the encryptionfeature can be enabled per pool:
# zpool get feature@encryption tankNAME PROPERTY VALUE SOURCEtank feature@encryption disabled local# zpool set feature@encryption=enabled# zpool get feature@encryption tankNAME PROPERTY VALUE SOURCEtank feature@encryption enabled local
| There is currently no support for booting from pools with encrypteddatasets using GRUB, and only limited support for automatically unlockingencrypted datasets on boot. Older versions of ZFS without encryption supportwill not be able to decrypt stored data. |
| It is recommended to either unlock storage datasets manually afterbooting, or to write a custom unit to pass the key material needed forunlocking on boot to zfs load-key. |
| Establish and test a backup procedure before enabling encryption ofproduction data. If the associated key material/passphrase/keyfile has beenlost, accessing the encrypted data is no longer possible. |
Encryption needs to be setup when creating datasets/zvols, and is inherited bydefault to child datasets. For example, to create an encrypted datasettank/encrypted_data and configure it as storage in Proxmox VE, run the followingcommands:
# zfs create -o encryption=on -o keyformat=passphrase tank/encrypted_dataEnter passphrase:Re-enter passphrase:# pvesm add zfspool encrypted_zfs -pool tank/encrypted_data
All guest volumes/disks create on this storage will be encrypted with theshared key material of the parent dataset.
To actually use the storage, the associated key material needs to be loadedand the dataset needs to be mounted. This can be done in one step with:
# zfs mount -l tank/encrypted_dataEnter passphrase for 'tank/encrypted_data':
It is also possible to use a (random) keyfile instead of prompting for apassphrase by setting the keylocation and keyformat properties, either atcreation time or with zfs change-key on existing datasets:
# dd if=/dev/urandom of=/path/to/keyfile bs=32 count=1# zfs change-key -o keyformat=raw -o keylocation=file:///path/to/keyfile tank/encrypted_data
| When using a keyfile, special care needs to be taken to secure thekeyfile against unauthorized access or accidental loss. Without the keyfile, itis not possible to access the plaintext data! |
A guest volume created underneath an encrypted dataset will have itsencryptionroot property set accordingly. The key material only needs to beloaded once per encryptionroot to be available to all encrypted datasetsunderneath it.
See the encryptionroot, encryption, keylocation, keyformat andkeystatus properties, the zfs load-key, zfs unload-key and zfschange-key commands and the Encryption section from man zfs for moredetails and advanced usage.
Compression in ZFS
When compression is enabled on a dataset, ZFS tries to compress all newblocks before writing them and decompresses them on reading. Alreadyexisting data will not be compressed retroactively.
You can enable compression with:
# zfs set compression=<algorithm> <dataset>
We recommend using the lz4 algorithm, because it adds very little CPUoverhead. Other algorithms like lzjb and gzip-N, where N is aninteger from 1 (fastest) to 9 (best compression ratio), are alsoavailable. Depending on the algorithm and how compressible the data is,having compression enabled can even increase I/O performance.
You can disable compression at any time with:
# zfs set compression=off <dataset>
Again, only new blocks will be affected by this change.
ZFS Special Device
Since version 0.8.0 ZFS supports special devices. A special device in apool is used to store metadata, deduplication tables, and optionally smallfile blocks.
A special device can improve the speed of a pool consisting of slow spinninghard disks with a lot of metadata changes. For example workloads that involvecreating, updating or deleting a large number of files will benefit from thepresence of a special device. ZFS datasets can also be configured to storewhole small files on the special device which can further improve theperformance. Use fast SSDs for the special device.
| The redundancy of the special device should match the one of thepool, since the special device is a point of failure for the whole pool. |
| Adding a special device to a pool cannot be undone! |
Create a pool with
specialdevice and RAID-1:
# zpool create -f -o ashift=12 <pool> mirror <device1> <device2> special mirror <device3> <device4>
Add a
specialdevice to an existing pool with RAID-1:
# zpool add <pool> special mirror <device1> <device2>
ZFS datasets expose the special_small_blocks=<size> property. size can be0 to disable storing small file blocks on the special device or a power oftwo in the range between 512B to 1M. After setting the property new fileblocks smaller than size will be allocated on the special device.
| If the value for special_small_blocks is greater than or equal tothe recordsize (default 128K) of the dataset, all data will be written tothe special device, so be careful! |
Setting the special_small_blocks property on a pool will change the defaultvalue of that property for all child ZFS datasets (for example all containersin the pool will opt in for small file blocks).
Opt in for all file smaller than 4K-blocks pool-wide:
# zfs set special_small_blocks=4K <pool>
Opt in for small file blocks for a single dataset:
# zfs set special_small_blocks=4K <pool>/<filesystem>
Opt out from small file blocks for a single dataset:
# zfs set special_small_blocks=0 <pool>/<filesystem>
ZFS Pool Features
Changes to the on-disk format in ZFS are only made between major version changesand are specified through features. All features, as well as the generalmechanism are well documented in the zpool-features(5) manpage.
Since enabling new features can render a pool not importable by an older versionof ZFS, this needs to be done actively by the administrator, by runningzpool upgrade on the pool (see the zpool-upgrade(8) manpage).
Unless you need to use one of the new features, there is no upside to enablingthem.
In fact, there are some downsides to enabling new features:
A system with root on ZFS, that still boots using GRUB will become unbootable if a new feature is active on the rpool, due to the incompatible implementation of ZFS in GRUB.
The system will not be able to import any upgraded pool when booted with an older kernel, which still ships with the old ZFS modules.
Booting an older Proxmox VE ISO to repair a non-booting system will likewise not work.
| Do not upgrade your rpool if your system is still booted withGRUB, as this will render your system unbootable. This includes systemsinstalled before Proxmox VE 5.4, and systems booting with legacy BIOS boot (seehow to determine the bootloader). |
Enable new features for a ZFS pool:
# zpool upgrade <pool>
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