Storage: ZFS

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Introduction

ZFS is a combined file system and logical volume manager designed by Sun Microsystems. Starting with Proxmox VE 3.4, the native Linux kernel port of the ZFS filesystem is introduced as optional file-system and also as an additional selection for the root file-system. There is no need for manually compiling ZFS, all packages are included (for both kernel branches, 2.6.32 and 3.10).

By using ZFS, its possible to achieve maximal 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.

In the first release, there are two ways to use ZFS on Proxmox VE:

  • as an local directory, supports all storage content types (instead of ext3 or ext4)
  • as zvol block-storage, currently supporting kvm images in raw format (new ZFS storage plugin)
    • The advantage of zvol is the snapshot capability on fs-level (fast)

This articles describes how to use ZFS on Proxmox VE.

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 and RAIDZ-3
  • Can use SSD for cache
  • Self healing
  • Continuous integrity checking
  • Designed for high storage capacities
  • Protection against data corruption
  • Asynchrony replication over network
  • Open Source
  • Encryption
  • ...

Hardware

ZFS depends heavily on memory, so you need at least 4GB to start. In practice, use as much you can get for your hardware/budget. To prevent data corruption, the use of high quality ECC RAM is very recommended.

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 quite significantly.

If you are experimenting with an installation of Proxmox inside a VM (Nested_Virtualization), don't use Virtio for disks of that VM, since are not supported by ZFS, use IDE or SCSI (it's ok also with Virtio type contorller) instead.

IMPORTANT: Do not use zfs on top of hardware controller which has it's 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).

Installation as root file-system

Screen-ISO-Install-ZFS.png

When you install with Proxmox-VE installer grater than 3.4. you can choose what FS you prefer.

It is not possible to use ZFS as rpool(root partition) with UEFI boot.

Administration

Create a new ZPool

To create a zfspool, 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-name> <device>

To activate the compression 

zfs set compression=lz4 <pool-name>

Create a new pool with RAID-0

Minimum 1 Disk 

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

Create a new pool with RAID-1

Minimum 2 Disks 

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

Create a new pool with RAID-10

Minimum 4 Disks 

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

Create a new pool with RAIDZ-1

Minimum 3 Disks 

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

Create a new pool with RAIDZ-2

Minimum 4 Disks 

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

Create a new pool with Cache and Log on one Disk

It is possible to create ZIL and L2ARC on one SSD. First partition the SSD in 2 partition with parted or gdisk (important: use GPT partition table).

As <device> it is possible to use more devices, like it's shown in "Create a new pool with RAID*". Important: identify device with /dev/disk/by-id/scsi-*<device> 

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

Minimum 1 Disk 

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

Activate Email notification

ZFS >=0.64 has an Email notification daemon. The daemon send an Email on zfs event like pool errors.

to activate the daemon it is necessary to edit /etc/zfs/zed.d/zed.rc with your favored editor.

Important: the only settings what is required is ZED_EMAIL the other are optional.

Add Cache and Log to existing pool

If you have an pool without cache and log. First partition the SSD in 2 partition with parted or gdisk (important: use GPT partition table).

Important: identify device with /dev/disk/by-id/scsi-*<device> 

zpool add -f <pool-name> cache <device1.part1> log <device1.part2>

Example: Proxmox with zfs as rootFS 

zpool add -f rpool cache /dev/disk/by-id/scsi-0QEMU_QEMU_HARDDISK_drive-scsi2-part1 \
log /dev/disk/by-id/scsi-0QEMU_QEMU_HARDDISK_drive-scsi2-part2

Changing a failed Device

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

Using ZFS Storage Plugin (via Proxmox VE GUI or shell)

If the zpool is created, you can use it on Proxmox VE GUI and CLI.

Adding a ZFS storage via GUI

Screen-Add-ZFS1.png
Screen-Add-ZFS2.png

Go to Datacenter/Storage and use the ZFSStorage plugin to add your zpool (select ZFS).

  • ID is for identification of the Storage
  • the checkbox ZFS Pool shows all existing pools (use CLI to create more)
  • Thin provisioning: allocate not all space immediately by creating virtual disks

Adding a ZFS storage via CLI

To create it by CLI use 

pvesm add zfspool <storage-ID> -pool <pool-name>

Adding ZFS root file-system as storage with Plugin

If you install Proxmox with ZFS and then create qcow2 VMs, you will have a "copy on write" image disk (qcow2) that writes on a "copy on write" file system (ZFS), that is not ideal for performance. To avoid it, thanks to the flexibility of ZFS, you can create an additional file system on the default storage pool and, thanks to the ZFS Plugin, use it as storage and have VMs disks created as volumes (block devices) on top of ZFS. To have this do the following: Create a new filesystem, that we will call "zfsdisks" in this example, from shell: 

zfs create rpool/zfsdisks

Now add it to the storage (Datacenter -> [Storage] -> Add, choose "ZFS", ad ID let's call it, for example, "zfsvols", as "ZFS Pool" choose "rpool/zfsdisks", set "thin provisioning" and you are ok. When you create a VM choose "zfsvols" as storage. 

cat /etc/pve/storage.cfg
zfspool: zfsvols
       pool rpool/zfsdisks
       content images,rootdir
       sparse

If you want to add the storage from the shell, you will have the same result (even if /etc/pve/storage.cfg does not exists yet) with 

pvesm add zfspool zfsvols -pool rpool/zfsdisks -content images,rootdir -sparse

With a VM 100 and one disk you will have something like that 

# zfs list
NAME                           USED  AVAIL  REFER  MOUNTPOINT
rpool                         4.78G  26.0G    96K  /rpool
rpool/ROOT                     676M  26.0G    96K  /rpool/ROOT
rpool/ROOT/pve-1               676M  26.0G   676M  /
rpool/swap                    4.12G  30.1G    64K  -
rpool/zfsdisks                 160K  26.0G    96K  /rpool/zfsdisks
rpool/zfsdisks/vm-100-disk-1    64K  26.0G    64K  -

so you see that it's a "block device" and thin provisioning is used (USED 64K)

Limit ZFS memory usage

It is good to use max 50 percent (which is default) of the system memory for ZFS arc to prevent performance shortage of the host.

Use your preferred editor to change the config in /etc/modprobe.d/zfs.conf and insert: 

options zfs zfs_arc_max=4299967296

This example setting limits the usage to 4GB.

IMPORTANT: If your root fs is ZFS you must update your initramfs every time this value changes. 

update-initramfs -u

If your Server has enough memory (i.e. you do not over commit memory) and you have a SWAP partition on ZFS lower the swappiness value to avoid problems and hang ups, a good value for servers is 10: 

sysctl -w vm.swappiness=10

Misc

QEMU tuning

see thread on proxmox forum, per user Nemesiz:

  • pool:
zfs set primarycache=all tank
  • kvm config:
  • change cache to Write Back
You can do it using web GUI or manually. Example:
ide0: data_zfs:100/vm-100-disk-1.raw,cache=writeback

if not set this happened: 

qm start 4016
kvm: -drive file=/data/pve-storage/images/4016/vm-4016-disk-1.raw,if=none,id=drive-virtio1,aio=native,cache=none: could not open disk image /data/pve-storage/images/4016/vm-4016-disk-1.raw: Invalid argument

(On PVE 4.x, you may also see warnings about the filesystem not supporting O_DIRECT.)

Example configurations for running Proxmox VE with ZFS

Install on a high performance system

As of 2013 and later, high performance servers have 16-64 cores, 256GB-1TB RAM and potentially many 2.5" disks and/or a PCIe based SSD with half a million IOPS. High performance systems benefit from a number of custom settings, for example enabling compression typically improves performance.

  • If you have a good number of disks keep organized by using aliases. Edit /etc/zfs/vdev_id.conf to prepare aliases for disk devices found in /dev/disk/by-id/ :
# run 'udevadm trigger' after updating this file
alias a0        scsi-36848f690e856b10018cdf39854055206
alias b0        scsi-36848f690e856b10018cdf3ce573fdeb6
alias a1        scsi-36848f690e856b10018cdf40f5b277cbc
alias b1        scsi-36848f690e856b10018cdf43a5db1b99b
alias a2        scsi-36848f690e856b10018cdf4575f652ad0
alias b2        scsi-36848f690e856b10018cdf47761587cec

Use flash for caching/logs. If you have only one SSD, use parted of gdisk to create a small partition for the ZIL (ZFS intent log) and a larger one for the L2ARC (ZFS read cache on disk). Make sure that the ZIL is on the first partition. In our case we have a Express Flash PCIe SSD with 175GB capacity and setup a ZIL with 25GB and a L2ARC cache partition of 150GB.

  • edit /etc/modprobe.d/zfs.conf​ to apply several tuning options for high performance servers:
# ZFS tuning for a proxmox machine that reserves 64GB for ZFS
#
# Don't let ZFS use less than 4GB and more than 64GB
options zfs zfs_arc_min=4294967296
options zfs zfs_arc_max=68719476736
#
# disabling prefetch is no longer required
options zfs l2arc_noprefetch=0
  • create a zpool of striped mirrors (equivalent to RAID10) with log device and cache and always enable compression:
zpool create -o compression=on -f tank mirror a0 b0 mirror a1 b1 mirror a2 b2 log /dev/rssda1 cache /dev/rssda2​
  • ​​​​​​​​check the status of the newly created pool:
root@proxmox:/# zpool status
  pool: tank
 state: ONLINE
  scan: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        tank        ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            a0      ONLINE       0     0     0
            b0      ONLINE       0     0     0
          mirror-1  ONLINE       0     0     0
            a1      ONLINE       0     0     0
            b1      ONLINE       0     0     0
          mirror-2  ONLINE       0     0     0
            a2      ONLINE       0     0     0
            b2      ONLINE       0     0     0
        logs
          rssda1    ONLINE       0     0     0
        cache
          rssda2    ONLINE       0     0     0

errors: No known data errors

Using PVE 2.3 on a 2013 high performance system with ZFS you can install Windows Server 2012 Datacenter Edition with GUI in just under 4 minutes.

How to prevent lvm of scanning zvols

It is not necessary but to reduce confusion, when using lvm it is a good practice.

open the config file /etc/lvm/lvm.conf

and insert the following line 

filter = [ "r|/dev/zd*|" ]

Troubleshooting and known issues

ZFS packages are not installed

If you upgraded to 3.4 or later, zfsutils package is not installed. You can install it with apt: 

apt-get install zfsutils zfs-initramfs

Grub boot ZFS problem

  • Symptoms: stuck at boot with an blinking prompt.
  • Reason: If you ZFS raid it could happen that your mainboard does not initial all your disks correctly and Grub will wait for all RAID disk members - and fails. It can happen with more than 2 disks in ZFS RAID configuration - we saw this on some boards with ZFS RAID-0/RAID-10

ZFS mounting workaround

The default ZFS mount -a script runs too late in the boot process for most system scripts. The following helps to mount ZFS correctly. This is only necessary if you do not use ZFS as root file-system and if you use ZFS as an additional directory storage.

2014-01-22: the info below came from this excellent wiki page: http://wiki.complete.org/ConvertingToZFS

  • Edit /etc/default/zfs and set ZFS_MOUNT='yes'
  • edit /etc/insserv.conf,
and at the end of the $local_fs line,
add zfs-mount (without a plus).
#
# All local file-systems are mounted (done during boot phase)
#
$local_fs       +mountall +mountall-bootclean +mountoverflowtmp +umountfs

edit /etc/init.d/zfs-mount and find three lines near the top, changing them like this: 

# Required-Start:
# Required-Stop:
# Default-Start: S

note remove the Required-Start and -Stop entries.

  • Activating init.d changes Then run:
insserv -v -d zfs-mount

I had an issue with pve storage on ZFS, before pve would start before ZFS and create directories at the ZFS mount point. To fix that start single user mode and remove the directories [ make sure they are empty.... ].

also see https://github.com/zfsonlinux/pkg-zfs/issues/101

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. To work around this follow #Limit ZFS memory usage and especially lower the vm.swappiness value.

Snapshot of LXC on ZFS

If you can't create a snapshot of an LXC container on ZFS and you get following message: 

INFO: rsync: set_acl: sys_acl_set_file(archiv, ACL_TYPE_DEFAULT): Operation not supported (95)

you can run following commands 

zfs create -o mountpoint=/mnt/vztmp rpool/vztmp
zfs set acltype=posixacl rpool/vztmp

Now set /mnt/vztmp in your /etc/vzdump.conf for tmp

Glossary

  • ZPool is the logical unit of the underlying disks, what zfs use.
  • ZVol is an emulated Block Device provided by ZFS
  • ZIL is ZFS Intent Log
  • ARC is Adaptive Replacement Cache and located in Ram
  • L2ARC is Layer2 Adaptive Replacement Cache and should be on an fast device (like SSD).

Further readings about ZFS

and this has some very important information to know before implementing zfs on a production system.

Very well written manual pages 

man zfs
man zpool
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