local-zfs.adoc

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