local-zfs.adoc

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