.. _chapter-zfs: ZFS on Linux ------------ ZFS is a combined file system and logical volume manager, designed by Sun Microsystems. There is no need to manually compile ZFS modules - all packages are included. By using ZFS, it's possible to achieve maximum enterprise features with low budget hardware, and also high performance systems by leveraging SSD caching or even SSD only setups. ZFS can replace expensive hardware raid cards with moderate CPU and memory load, combined with easy management. General advantages of ZFS: * Easy configuration and management with 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 * Asynchronous replication over network * Open Source * Encryption Hardware ~~~~~~~~~ ZFS depends heavily on memory, so it's recommended to have 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 an enterprise class SSD (for example, Intel SSD DC S3700 Series). This can increase the overall performance significantly. IMPORTANT: Do not use ZFS on top of a hardware controller which has its own cache management. ZFS needs to directly communicate with disks. An HBA adapter or something like an LSI controller flashed in ``IT`` mode is recommended. 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 extensive manual pages, which can be read with: .. code-block:: console # 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. .. code-block:: console # zpool create -f -o ashift=12 Create a new pool with RAID-0 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Minimum 1 disk .. code-block:: console # zpool create -f -o ashift=12 Create a new pool with RAID-1 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Minimum 2 disks .. code-block:: console # zpool create -f -o ashift=12 mirror Create a new pool with RAID-10 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Minimum 4 disks .. code-block:: console # zpool create -f -o ashift=12 mirror mirror Create a new pool with RAIDZ-1 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Minimum 3 disks .. code-block:: console # zpool create -f -o ashift=12 raidz1 Create a new pool with RAIDZ-2 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Minimum 4 disks .. code-block:: console # zpool create -f -o ashift=12 raidz2 Create a new pool with cache (L2ARC) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ It is possible to use a dedicated cache drive partition to increase the performance (use SSD). For ``, you can use multiple devices, as is shown in "Create a new pool with RAID*". .. code-block:: console # zpool create -f -o ashift=12 cache Create a new pool with log (ZIL) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ It is possible to use a dedicated cache drive partition to increase the performance (SSD). For ``, you can use multiple devices, as is shown in "Create a new pool with RAID*". .. code-block:: console # zpool create -f -o ashift=12 log Add cache and log to an existing pool ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ You can add cache and log devices to a pool after its creation. In this example, we will use a single drive for both cache and log. First, you need to create 2 partitions on the SSD 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. .. code-block:: console # zpool add -f log cache Changing a failed device ^^^^^^^^^^^^^^^^^^^^^^^^ .. code-block:: console # zpool replace -f Changing a failed bootable device ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Depending on how Proxmox Backup was installed, it is either using `grub` or `systemd-boot` as a bootloader. In either case, the first steps of copying the partition table, reissuing GUIDs and replacing the 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. .. code-block:: console # sgdisk -R # sgdisk -G # zpool replace -f .. NOTE:: Use the `zpool status -v` command to monitor how far the resilvering process of the new disk has progressed. With `systemd-boot`: .. code-block:: console # proxmox-boot-tool format # proxmox-boot-tool init .. NOTE:: `ESP` stands for EFI System Partition, which is setup as partition #2 on bootable disks setup by the `Proxmox Backup`_ installer. For details, see :ref:`Setting up a new partition for use as synced ESP `. With `grub`: Usually `grub.cfg` is located in `/boot/grub/grub.cfg` .. code-block:: console # grub-install # grub-mkconfig -o /path/to/grub.cfg Activate e-mail notification ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ZFS comes with an event daemon ``ZED``, which monitors events generated by the ZFS kernel module. The daemon can also send emails on ZFS events like pool errors. Newer ZFS packages ship the daemon in a separate package ``zfs-zed``, which should already be installed by default in `Proxmox Backup`_. You can configure the daemon via the file ``/etc/zfs/zed.d/zed.rc`` with your favorite editor. The required setting for email notfication is ``ZED_EMAIL_ADDR``, which is set to ``root`` by default. .. code-block:: console ZED_EMAIL_ADDR="root" Please note that `Proxmox Backup`_ forwards mails to `root` to the email address configured for the root user. 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 degradation of the host. Use your preferred editor to change the configuration in `/etc/modprobe.d/zfs.conf` and insert: .. code-block:: console options zfs zfs_arc_max=8589934592 The above example limits the usage to 8 GiB ('8 * 2^30^'). .. IMPORTANT:: In case your desired `zfs_arc_max` value is lower than or equal to `zfs_arc_min` (which defaults to 1/32 of the system memory), `zfs_arc_max` will be ignored. Thus, for it to work in this case, you must set `zfs_arc_min` to at most `zfs_arc_max - 1`. This would require updating the configuration in `/etc/modprobe.d/zfs.conf`, with: .. code-block:: console options zfs zfs_arc_min=8589934591 options zfs zfs_arc_max=8589934592 This example setting limits the usage to 8 GiB ('8 * 2^30^') on systems with more than 256 GiB of total memory, where simply setting `zfs_arc_max` alone would not work. .. IMPORTANT:: If your root file system is ZFS, you must update your initramfs every time this value changes. .. code-block:: console # update-initramfs -u Swap on ZFS ^^^^^^^^^^^ Swap-space created on a zvol may cause some issues, such as blocking the server or generating a high IO load. We strongly recommend using enough memory, so that you normally do not run into low memory situations. Should you need or want to add swap, it is preferred 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 the installer. Additionally, you can lower the `swappiness` value. A good value for servers is 10: .. code-block:: console # 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: .. code-block:: console vm.swappiness = 10 .. table:: Linux kernel `swappiness` parameter values :widths:auto ==================== =============================================================== 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 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. ==================== =============================================================== ZFS compression ^^^^^^^^^^^^^^^ To activate compression: .. code-block:: console # zpool set compression=lz4 We recommend using the `lz4` algorithm, since it adds very little CPU overhead. Other algorithms such as `lzjb`, `zstd` and `gzip-N` (where `N` is an integer from `1-9` representing the compression ratio, where 1 is fastest and 9 is best compression) are also available. 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: .. code-block:: console # zfs set compression=off Only new blocks will be affected by this change. .. _local_zfs_special_device: ZFS special device ^^^^^^^^^^^^^^^^^^ Since version 0.8.0, ZFS supports `special` devices. A `special` device in a pool is used to store metadata, deduplication tables, and optionally small file blocks. A `special` device can improve the speed of a pool consisting of slow spinning hard disks with a lot of metadata changes. For example, workloads that involve creating, updating or deleting a large number of files will benefit from the presence of a `special` device. ZFS datasets can also be configured to store small files on the `special` device, which can further improve the performance. Use fast SSDs for the `special` device. .. IMPORTANT:: The redundancy of the `special` device should match the one of the pool, since the `special` device is a point of failure for the entire pool. .. WARNING:: Adding a `special` device to a pool cannot be undone! To create a pool with `special` device and RAID-1: .. code-block:: console # zpool create -f -o ashift=12 mirror special mirror Adding a `special` device to an existing pool with RAID-1: .. code-block:: console # zpool add special mirror ZFS datasets expose the `special_small_blocks=` property. `size` can be `0` to disable storing small file blocks on the `special` device, or a power of two in the range between `512B` to `128K`. After setting this property, new file blocks smaller than `size` will be allocated on the `special` device. .. IMPORTANT:: If the value for `special_small_blocks` is greater than or equal to the `recordsize` (default `128K`) of the dataset, *all* data will be written to the `special` device, so be careful! Setting the `special_small_blocks` property on a pool will change the default value of that property for all child ZFS datasets (for example, all containers in the pool will opt in for small file blocks). Opt in for all files smaller than 4K-blocks pool-wide: .. code-block:: console # zfs set special_small_blocks=4K Opt in for small file blocks for a single dataset: .. code-block:: console # zfs set special_small_blocks=4K / Opt out from small file blocks for a single dataset: .. code-block:: console # zfs set special_small_blocks=0 / Troubleshooting ^^^^^^^^^^^^^^^ Corrupt cache file """""""""""""""""" `zfs-import-cache.service` imports ZFS pools using the ZFS cache file. If this file becomes corrupted, the service won't be able to import the pools that it's unable to read from it. As a result, in case of a corrupted ZFS cache file, some volumes may not be mounted during boot and must be mounted manually later. For each pool, run: .. code-block:: console # zpool set cachefile=/etc/zfs/zpool.cache POOLNAME then, update the `initramfs` by running: .. code-block:: console # update-initramfs -u -k all and finally, reboot the node. Another workaround to this problem is enabling the `zfs-import-scan.service`, which searches and imports pools via device scanning (usually slower).