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1ZFS on Linux
2------------
3include::attributes.txt[]
4
5ZFS is a combined file system and logical volume manager designed by
6Sun Microsystems. Starting with {pve} 3.4, the native Linux
7kernel port of the ZFS file system is introduced as optional
8file-system and also as an additional selection for the root
9file-system. There is no need for manually compile ZFS modules - all
10packages are included.
11
12By using ZFS, its possible to achieve maximal enterprise features with
13low budget hardware, but also high performance systems by leveraging
14SSD caching or even SSD only setups. ZFS can replace cost intense
15hardware raid cards by moderate CPU and memory load combined with easy
16management.
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
53Hardware
54~~~~~~~~
55
56ZFS depends heavily on memory, so you need at least 8GB to start. In
57practice, use as much you can get for your hardware/budget. To prevent
58data corruption, we recommend the use of high quality ECC RAM.
59
60If you use a dedicated cache and/or log disk, you should use a
61enterprise class SSD (e.g. Intel SSD DC S3700 Series). This can
62increase the overall performance significantly.
63
64IMPORTANT: Do not use ZFS on top of hardware controller which has it's
65own cache management. ZFS needs to directly communicate with disks. An
66HBA adapter is the way to go, or something like LSI controller flashed
67in 'IT' mode.
68
69If you are experimenting with an installation of {pve} inside a VM
70(Nested Virtualization), don't use 'virtio' for disks of that VM,
71since they are not supported by ZFS. Use IDE or SCSI instead (works
72also with 'virtio' SCSI controller type).
73
74
75Installation as root file system
76~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
77
78When you install using the {pve} installer, you can choose ZFS for the
79root file system. You need to select the RAID type at installation
80time:
81
82[horizontal]
83RAID0:: Also called 'striping'. The capacity of such volume is the sum
84of the capacity of all disks. But RAID0 does not add any redundancy,
85so the failure of a single drive makes the volume unusable.
86
87RAID1:: Also called mirroring. Data is written identically to all
88disks. This mode requires at least 2 disks with the same size. The
89resulting capacity is that of a single disk.
90
91RAID10:: A combination of RAID0 and RAID1. Requires at least 4 disks.
92
93RAIDZ-1:: A variation on RAID-5, single parity. Requires at least 3 disks.
94
95RAIDZ-2:: A variation on RAID-5, double parity. Requires at least 4 disks.
96
97RAIDZ-3:: A variation on RAID-5, triple parity. Requires at least 5 disks.
98
99The installer automatically partitions the disks, creates a ZFS pool
100called 'rpool', and installs the root file system on the ZFS subvolume
101'rpool/ROOT/pve-1'.
102
103Another subvolume called 'rpool/data' is created to store VM
104images. In order to use that with the {pve} tools, the installer
105creates the following configuration entry in '/etc/pve/storage.cfg':
106
107----
108zfspool: local-zfs
109 pool rpool/data
110 sparse
111 content images,rootdir
112----
113
114After 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
122config:
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
133errors: No known data errors
134----
135
136The 'zfs' command is used configure and manage your ZFS file
137systems. The following command lists all file systems after
138installation:
139
140----
141# zfs list
142NAME USED AVAIL REFER MOUNTPOINT
143rpool 4.94G 7.68T 96K /rpool
144rpool/ROOT 702M 7.68T 96K /rpool/ROOT
145rpool/ROOT/pve-1 702M 7.68T 702M /
146rpool/data 96K 7.68T 96K /rpool/data
147rpool/swap 4.25G 7.69T 64K -
148----
149
150
151Bootloader
152~~~~~~~~~~
153
154The default ZFS disk partitioning scheme does not use the first 2048
155sectors. This gives enough room to install a GRUB boot partition. The
156{pve} installer automatically allocates that space, and installs the
157GRUB boot loader there. If you use a redundant RAID setup, it installs
158the boot loader on all disk required for booting. So you can boot
159even if some disks fail.
160
161NOTE: It is not possible to use ZFS as root partition with UEFI
162boot.
163
164
165ZFS Administration
166~~~~~~~~~~~~~~~~~~
167
168This section gives you some usage examples for common tasks. ZFS
169itself is really powerful and provides many options. The main commands
170to manage ZFS are 'zfs' and 'zpool'. Both commands comes with great
171manual pages, worth to read:
172
173----
174# man zpool
175# man zfs
176-----
177
178.Create a new ZPool
179
180To create a new pool, at least one disk is needed. The 'ashift' should
181have the same sector-size (2 power of 'ashift') or larger as the
182underlying disk.
183
184 zpool create -f -o ashift=12 <pool> <device>
185
186To activate the compression
187
188 zfs set compression=lz4 <pool>
189
190.Create a new pool with RAID-0
191
192Minimum 1 Disk
193
194 zpool create -f -o ashift=12 <pool> <device1> <device2>
195
196.Create a new pool with RAID-1
197
198Minimum 2 Disks
199
200 zpool create -f -o ashift=12 <pool> mirror <device1> <device2>
201
202.Create a new pool with RAID-10
203
204Minimum 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
210Minimum 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
216Minimum 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
222It is possible to use a dedicated cache drive partition to increase
223the performance (use SSD).
224
225As '<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
232It is possible to use a dedicated cache drive partition to increase
233the performance(SSD).
234
235As '<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
242If you have an pool without cache and log. First partition the SSD in
2432 partition with parted or gdisk
244
245IMPORTANT: Always use GPT partition tables (gdisk or parted).
246
247The maximum size of a log device should be about half the size of
248physical memory, so this is usually quite small. The rest of the SSD
249can 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
258Activate E-Mail Notification
259~~~~~~~~~~~~~~~~~~~~~~~~~~~~
260
261ZFS comes with an event daemon, which monitors events generated by the
262ZFS kernel module. The daemon can also send E-Mails on ZFS event like
263pool errors.
264
265To 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
267ZED_EMAIL_ADDR="root"
268
269Please note {pve} forwards mails to 'root' to the email address
270configured for the root user.
271
272IMPORTANT: the only settings that is required is ZED_EMAIL_ADDR. All
273other settings are optional.
274
275
276Limit ZFS memory usage
277~~~~~~~~~~~~~~~~~~~~~~
278
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279It is good to use maximal 50 percent (which is the default) of the
280system memory for ZFS ARC to prevent performance shortage of the
281host. Use your preferred editor to change the configuration in
282/etc/modprobe.d/zfs.conf and insert:
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283
284 options zfs zfs_arc_max=8589934592
285
286This example setting limits the usage to 8GB.
287
288[IMPORTANT]
289====
290If your root fs is ZFS you must update your initramfs every
291time this value changes.
292
293 update-initramfs -u
294====
295
296
297.SWAP on ZFS
298
299SWAP on ZFS on Linux may generate some troubles, like blocking the
300server or generating a high IO load, often seen when starting a Backup
301to an external Storage.
302
303We strongly recommend to use enough memory, so that you normally do not
304run 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
309To make the swappiness persistence, open '/etc/sysctl.conf' with
310an 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
319an 'out of memory' condition
320| vm.swappiness = 1 | Minimum amount of swapping without
321disabling it entirely.
322| vm.swappiness = 10 | This value is sometimes recommended to
323improve 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|===========================================================