local-zfs.adoc

   1 [[chapter_zfs]]
   2 ZFS on Linux
   3 ------------
   4 ifdef::wiki[]
   5 :pve-toplevel:
   6 endif::wiki[]
   7
   8 ZFS is a combined file system and logical volume manager designed by
   9 Sun Microsystems. Starting with {pve} 3.4, the native Linux
  10 kernel port of the ZFS file system is introduced as optional
  11 file system and also as an additional selection for the root
  12 file system. There is no need for manually compile ZFS modules - all
  13 packages are included.
  14
  15 By using ZFS, its possible to achieve maximum enterprise features with
  16 low budget hardware, but also high performance systems by leveraging
  17 SSD caching or even SSD only setups. ZFS can replace cost intense
  18 hardware raid cards by moderate CPU and memory load combined with easy
  19 management.
  20
  21 .General ZFS advantages
  22
  23 * Easy configuration and management with {pve} GUI and CLI.
  24
  25 * Reliable
  26
  27 * Protection against data corruption
  28
  29 * Data compression on file system level
  30
  31 * Snapshots
  32
  33 * Copy-on-write clone
  34
  35 * Various raid levels: RAID0, RAID1, RAID10, RAIDZ-1, RAIDZ-2 and RAIDZ-3
  36
  37 * Can use SSD for cache
  38
  39 * Self healing
  40
  41 * Continuous integrity checking
  42
  43 * Designed for high storage capacities
  44
  45 * Protection against data corruption
  46
  47 * Asynchronous replication over network
  48
  49 * Open Source
  50
  51 * Encryption
  52
  53 * ...
  54
  55
  56 Hardware
  57 ~~~~~~~~
  58
  59 ZFS depends heavily on memory, so you need at least 8GB to start. In
  60 practice, use as much you can get for your hardware/budget. To prevent
  61 data corruption, we recommend the use of high quality ECC RAM.
  62
  63 If you use a dedicated cache and/or log disk, you should use an
  64 enterprise class SSD (e.g. Intel SSD DC S3700 Series). This can
  65 increase the overall performance significantly.
  66
  67 IMPORTANT: Do not use ZFS on top of hardware controller which has its
  68 own cache management. ZFS needs to directly communicate with disks. An
  69 HBA adapter is the way to go, or something like LSI controller flashed
  70 in ``IT'' mode.
  71
  72 If you are experimenting with an installation of {pve} inside a VM
  73 (Nested Virtualization), don't use `virtio` for disks of that VM,
  74 since they are not supported by ZFS. Use IDE or SCSI instead (works
  75 also with `virtio` SCSI controller type).
  76
  77
  78 Installation as Root File System
  79 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  80
  81 When you install using the {pve} installer, you can choose ZFS for the
  82 root file system. You need to select the RAID type at installation
  83 time:
  84
  85 [horizontal]
  86 RAID0:: Also called ``striping''. The capacity of such volume is the sum
  87 of the capacities of all disks. But RAID0 does not add any redundancy,
  88 so the failure of a single drive makes the volume unusable.
  89
  90 RAID1:: Also called ``mirroring''. Data is written identically to all
  91 disks. This mode requires at least 2 disks with the same size. The
  92 resulting capacity is that of a single disk.
  93
  94 RAID10:: A combination of RAID0 and RAID1. Requires at least 4 disks.
  95
  96 RAIDZ-1:: A variation on RAID-5, single parity. Requires at least 3 disks.
  97
  98 RAIDZ-2:: A variation on RAID-5, double parity. Requires at least 4 disks.
  99
 100 RAIDZ-3:: A variation on RAID-5, triple parity. Requires at least 5 disks.
 101
 102 The installer automatically partitions the disks, creates a ZFS pool
 103 called `rpool`, and installs the root file system on the ZFS subvolume
 104 `rpool/ROOT/pve-1`.
 105
 106 Another subvolume called `rpool/data` is created to store VM
 107 images. In order to use that with the {pve} tools, the installer
 108 creates the following configuration entry in `/etc/pve/storage.cfg`:
 109
 110 ----
 111 zfspool: local-zfs
 112         pool rpool/data
 113         sparse
 114         content images,rootdir
 115 ----
 116
 117 After installation, you can view your ZFS pool status using the
 118 `zpool` command:
 119
 120 ----
 121 # zpool status
 122   pool: rpool
 123  state: ONLINE
 124   scan: none requested
 125 config:
 126
 127         NAME        STATE     READ WRITE CKSUM
 128         rpool       ONLINE       0     0     0
 129           mirror-0  ONLINE       0     0     0
 130             sda2    ONLINE       0     0     0
 131             sdb2    ONLINE       0     0     0
 132           mirror-1  ONLINE       0     0     0
 133             sdc     ONLINE       0     0     0
 134             sdd     ONLINE       0     0     0
 135
 136 errors: No known data errors
 137 ----
 138
 139 The `zfs` command is used configure and manage your ZFS file
 140 systems. The following command lists all file systems after
 141 installation:
 142
 143 ----
 144 # zfs list
 145 NAME               USED  AVAIL  REFER  MOUNTPOINT
 146 rpool             4.94G  7.68T    96K  /rpool
 147 rpool/ROOT         702M  7.68T    96K  /rpool/ROOT
 148 rpool/ROOT/pve-1   702M  7.68T   702M  /
 149 rpool/data          96K  7.68T    96K  /rpool/data
 150 rpool/swap        4.25G  7.69T    64K  -
 151 ----
 152
 153
 154 Bootloader
 155 ~~~~~~~~~~
 156
 157 The default ZFS disk partitioning scheme does not use the first 2048
 158 sectors. This gives enough room to install a GRUB boot partition. The
 159 {pve} installer automatically allocates that space, and installs the
 160 GRUB boot loader there. If you use a redundant RAID setup, it installs
 161 the boot loader on all disk required for booting. So you can boot
 162 even if some disks fail.
 163
 164 NOTE: It is not possible to use ZFS as root file system with UEFI
 165 boot.
 166
 167
 168 ZFS Administration
 169 ~~~~~~~~~~~~~~~~~~
 170
 171 This section gives you some usage examples for common tasks. ZFS
 172 itself is really powerful and provides many options. The main commands
 173 to manage ZFS are `zfs` and `zpool`. Both commands come with great
 174 manual pages, which can be read with:
 175
 176 ----
 177 # man zpool
 178 # man zfs
 179 -----
 180
 181 .Create a new zpool
 182
 183 To create a new pool, at least one disk is needed. The `ashift` should
 184 have the same sector-size (2 power of `ashift`) or larger as the
 185 underlying disk.
 186
 187  zpool create -f -o ashift=12 <pool> <device>
 188
 189 To activate compression
 190
 191  zfs set compression=lz4 <pool>
 192
 193 .Create a new pool with RAID-0
 194
 195 Minimum 1 Disk
 196
 197  zpool create -f -o ashift=12 <pool> <device1> <device2>
 198
 199 .Create a new pool with RAID-1
 200
 201 Minimum 2 Disks
 202
 203  zpool create -f -o ashift=12 <pool> mirror <device1> <device2>
 204
 205 .Create a new pool with RAID-10
 206
 207 Minimum 4 Disks
 208
 209  zpool create -f -o ashift=12 <pool> mirror <device1> <device2> mirror <device3> <device4>
 210
 211 .Create a new pool with RAIDZ-1
 212
 213 Minimum 3 Disks
 214
 215  zpool create -f -o ashift=12 <pool> raidz1 <device1> <device2> <device3>
 216
 217 .Create a new pool with RAIDZ-2
 218
 219 Minimum 4 Disks
 220
 221  zpool create -f -o ashift=12 <pool> raidz2 <device1> <device2> <device3> <device4>
 222
 223 .Create a new pool with cache (L2ARC)
 224
 225 It is possible to use a dedicated cache drive partition to increase
 226 the performance (use SSD).
 227
 228 As `<device>` it is possible to use more devices, like it's shown in
 229 "Create a new pool with RAID*".
 230
 231  zpool create -f -o ashift=12 <pool> <device> cache <cache_device>
 232
 233 .Create a new pool with log (ZIL)
 234
 235 It is possible to use a dedicated cache drive partition to increase
 236 the performance(SSD).
 237
 238 As `<device>` it is possible to use more devices, like it's shown in
 239 "Create a new pool with RAID*".
 240
 241  zpool create -f -o ashift=12 <pool> <device> log <log_device>
 242
 243 .Add cache and log to an existing pool
 244
 245 If you have an pool without cache and log. First partition the SSD in
 246 2 partition with `parted` or `gdisk`
 247
 248 IMPORTANT: Always use GPT partition tables.
 249
 250 The maximum size of a log device should be about half the size of
 251 physical memory, so this is usually quite small. The rest of the SSD
 252 can be used as cache.
 253
 254  zpool add -f <pool> log <device-part1> cache <device-part2>
 255
 256 .Changing a failed device
 257
 258  zpool replace -f <pool> <old device> <new-device>
 259
 260
 261 Activate E-Mail Notification
 262 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 263
 264 ZFS comes with an event daemon, which monitors events generated by the
 265 ZFS kernel module. The daemon can also send emails on ZFS events like
 266 pool errors. Newer ZFS packages ships the daemon in a separate package,
 267 and you can install it using `apt-get`:
 268
 269 ----
 270 # apt-get install zfs-zed
 271 ----
 272
 273 To activate the daemon it is necessary to edit `/etc/zfs/zed.d/zed.rc` with your
 274 favourite editor, and uncomment the `ZED_EMAIL_ADDR` setting:
 275
 276 --------
 277 ZED_EMAIL_ADDR="root"
 278 --------
 279
 280 Please note {pve} forwards mails to `root` to the email address
 281 configured for the root user.
 282
 283 IMPORTANT: The only setting that is required is `ZED_EMAIL_ADDR`. All
 284 other settings are optional.
 285
 286
 287 Limit ZFS Memory Usage
 288 ~~~~~~~~~~~~~~~~~~~~~~
 289
 290 It is good to use at most 50 percent (which is the default) of the
 291 system memory for ZFS ARC to prevent performance shortage of the
 292 host. Use your preferred editor to change the configuration in
 293 `/etc/modprobe.d/zfs.conf` and insert:
 294
 295 --------
 296 options zfs zfs_arc_max=8589934592
 297 --------
 298
 299 This example setting limits the usage to 8GB.
 300
 301 [IMPORTANT]
 302 ====
 303 If your root file system is ZFS you must update your initramfs every
 304 time this value changes:
 305
 306  update-initramfs -u
 307 ====
 308
 309
 310 [[zfs_swap]]
 311 .SWAP on ZFS
 312
 313 Swap-space created on a zvol may generate some troubles, like blocking the
 314 server or generating a high IO load, often seen when starting a Backup
 315 to an external Storage.
 316
 317 We strongly recommend to use enough memory, so that you normally do not
 318 run into low memory situations. Should you need or want to add swap, it is
 319 preferred to create a partition on a physical disk and use it as swapdevice.
 320 You can leave some space free for this purpose in the advanced options of the
 321 installer. Additionally, you can lower the
 322 ``swappiness'' value. A good value for servers is 10:
 323
 324  sysctl -w vm.swappiness=10
 325
 326 To make the swappiness persistent, open `/etc/sysctl.conf` with
 327 an editor of your choice and add the following line:
 328
 329 --------
 330 vm.swappiness = 10
 331 --------
 332
 333 .Linux kernel `swappiness` parameter values
 334 [width="100%",cols="<m,2d",options="header"]
 335 |===========================================================
 336 | Value               | Strategy
 337 | vm.swappiness = 0   | The kernel will swap only to avoid
 338 an 'out of memory' condition
 339 | vm.swappiness = 1   | Minimum amount of swapping without
 340 disabling it entirely.
 341 | vm.swappiness = 10  | This value is sometimes recommended to
 342 improve performance when sufficient memory exists in a system.
 343 | vm.swappiness = 60  | The default value.
 344 | vm.swappiness = 100 | The kernel will swap aggressively.
 345 |===========================================================