1: # ZFS on NetBSD
2:
3: This page attempts to do two things: provide enough orientation and
4: pointers to standard ZFS documentation for NetBSD users who are new to
5: ZFS, and to describe NetBSD-specific ZFS information. It is
6: emphatically not a tutorial or an introduction to ZFS.
7:
8: Many things are marked with \todo because they need a better
9: explanation, and some have question marks
10:
11: # Status of ZFS in NetBSD
12:
13: ## NetBSD 8
14:
15: NetBSD 8 has an old version of ZFS, and it is not recommended for use
16: at all. There is no evidence that anyone is interested in helping
17: with ZFS on 8. Those wishing to use ZFS on NetBSD 8 should therefore
18: update to NetBSD 9.
19:
20: ## NetBSD 9
21:
22: NetBSD-9 has ZFS that is considered to work well. There have been
23: fixes since 9.0_RELEASE. As always, people running NetBSD 9 are
24: likely best served by the most recent version of the netbsd-9 stable
25: branch. As of 2021-02, ZFS in the NetBSD 9.1 release is very close to
26: netbsd-9.
27:
28: ## NetBSD-current
29:
30: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
31:
32: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
33: ffs and pivoting.
34:
35: ## NetBSD/xen special issues
36:
37: Summary: if you are using NetBSD, xen and zfs, use NetBSD-current.
38:
39: In NetBSD-9, MAXPHYS is 64KB in most places, but because of xbd(4) it
40: is set to 32KB for XEN kernels. Thus the standard zfs kernel modules
41: do not work under xen. In NetBSD-current, xbd(4) supports 64 KB
42: MAXPHYS and this is no longer an issue. Xen and zfs on current are
43: reported to work well together, as of 2021-02.
44:
45: ## Architectures
46:
47: Most people seem to be using amd64.
48:
49: To build zfs, one puts MKZFS=yes in mk.conf. This is default on amd64
50: and aarch64 on netbsd-9. In current, it is also default on sparc64.
51:
52: More or less, zfs can be enabled on an architecture when it is known
53: to build and run reliably. (Of course, users are welcome to build it
54: and report.)
55:
56: # Quick Start
57:
58: See the [FreeBSD Quickstart
59: Guide](https://www.freebsd.org/doc/handbook/zfs-quickstart.html); only
60: the first item is NetBSD specific.
61:
62: - Put zfs=YES in rc.conf.
63:
64: - Create a pool as "zpool create pool1 /dev/dk0".
65:
66: - df and see /pool1
67:
68: - Create a filesystem mounted on /n0 as "zfs create -o
69: mountpoint=/n0 pool1/n0".
70:
71: - Read the documentation referenced in the next section.
72:
73: ## Documentation Pointers
74:
75: See the man pages for zfs(8), zpool(8). Also see zdb(8), if only for
76: seeing pool config info when run with no arguments.
77:
78: - [OpenZFS Documentation](https://openzfs.github.io/openzfs-docs/)
79: - [OpenZFS admin docs index page](https://github.com/openzfs/zfs/wiki/Admin-Documentation)
80: - [FreeBSD Handbook ZFS Chapter](https://www.freebsd.org/doc/handbook/zfs.html)
81: - [Oracle ZFS Administration Manual](https://docs.oracle.com/cd/E26505_01/html/E37384/index.html)
82: - [Wikipedia](https://en.wikipedia.org/wiki/ZFS)
83:
84: # NetBSD-specific information
85:
86: ## rc.conf
87:
88: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
89: scripts bring up ZFS and mount ZFS file systems.
90:
91: ## pool locations
92:
93: One can add disks or parts of disks into pools. Methods of specifying
94: areas to be included include:
95:
96: - entire disks (e.g., /dev/wd0d on amd64, or /dev/wd0 which has the same major/minor)
97: - disklabel partitions (e.g., /dev/sd0e)
98: - wedges (e.g., /dev/dk0)
99:
100: Information about created or imported pools is stored in
101: /etc/zfs/zpool.cache.
102:
103: ## pool native blocksize mismatch
104:
105: ZFS attempts to find out the native blocksize for a disk when using it
106: in a pool; this is almost always 512 or 4096. Somewhere between 9.0
107: and 9.1, at least some disks on some controllers that used to report
108: 512 now report 4096. This provokes a blocksize mismatch warning.
109:
110: Given that the native blocksize of the disk didn't change, and things
111: seemed OK using the 512 emulated blocks, the warning is likely not
112: critical. However, it is also likely that rebuilding the pool with
113: the 4096 blocksize is likely to result in better behavior because ZFS
114: will only try to do 4096-byte writes. \todo Verify this and find the
115: actual change and explain better.
116:
117: ## pool importing problems
118:
119: While one can "zpool pool0 /dev/wd0f" and have a working pool, this
120: pool cannot be exported and imported straigthforwardly. "zpool
121: export" works fine, and deletes zpool.cache. "zpool import", however,
122: only looks at entire disks (e.g. /dev/wd0), and might look at slices
123: (e.g. /dev/dk0). It does not look at partitions like /dev/wd0f, and
124: there is no way on the command line to ask that specific devices be
125: examined. Thus, export/import fails for pools with disklabel
126: partitions.
127:
128: One can make wd0 be a link to wd0f temporarily, and the pool will then
129: be importable. However, "wd0" is stored in zpool.cache and on the
130: next boot that will attempt to be used. This is obviously not a good
131: approach.
132:
133: One an mkdir e.g. /etc/zfs/pool0 and in it have a symlink to
134: /dev/wd0f. Then, zpool import -d /etc/zfs/pool0 will scan
135: /etc/zfs/pool0/wd0f and succeed. The resulting zpool.cache will have
136: that path, but having symlinks in /etc/zfs/POOLNAME seems acceptable.
137:
138: \todo Determine a good fix, perhaps man page changes only, fix it
139: upstream, in curent, and in 9, before removing this discussion.
140:
141: ## mountpoint conventions
142:
143: By default, datasets are mounted as /poolname/datasetname. One can
144: also set a mountpoint; see zfs(8).
145:
146: There does not appear to be any reason to choose explicit mountpoints
147: vs the default (and either using data in place or symlinking to it).
148:
149: ## mount order
150:
151: NetBSD 9 mounts other file systems and then ZFS file systems. This can
152: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
153: NFS. A workaround is to use noauto and do the mounts in
154: /etc/rc.local.
155:
156: NetBSD current after 20200301 mounts ZFS first. The same issues and
157: workarounds apply in different circumstances.
158:
159: ## NFS
160:
161: zfs filesystems can be exported via NFS, simply by placing them in
162: /etc/exports like any other filesystem.
163:
164: The "zfs share" command adds a line for each filesystem with the
165: sharenfs property set to /etc/zfs/exports, and "zfs unshare" removes
166: it. This file is ignored on NetBSD-9 and current before 20210216; on
167: current after 20210216 those filesystems should be exported (assuming
168: NFS is enabled). It does not appear to be possible to set options
169: like maproot and network restrictions via this method.
170:
171: On current before 20210216, a remote mkdir of a filesystem mounted via
172: -maproot=0:10 causes a kernel NULL pointer dereference. This is now
173: fixed.
174:
175: ## zvol
176:
177: Within a ZFS pool, the standard approach is to have file systems, but
178: one can also create a zvol, which is a block device of a certain size.
179:
180: As an example, "zfs create -V 16G tank0/xen-netbsd-9-amd64" creates a
181: zvol (intended to be a virtual disk for a domU).
182:
183: The zvol in the example will appear as
184: /dev/zvol/rdsk/tank0/xen-netbsd-9-amd64 and
185: /dev/zvol/dsk/tank0/xen-netbsd-9-amd64 and can be used like a
186: disklabel partition or wedge. However, the system will not read
187: disklabels and gpt labels from a zvol.
188:
189: Doing "swapctl -a" on a zvol device node fails. \todo Is it really
190: true that NetBSD can't swap on a zvol?
191:
192: \todo Explain that one can export a zvol via iscsi.
193:
194: One can use ccd to create a normal-looking disk from a zvol. This
195: allows reading a GPT label from the zvol, which is useful in case the
196: zvol had been exported via iscsi and some other system created a
197: label.
198:
199: # Memory usage
200:
201: Basically, ZFS uses lots of memory and most people run it on systems
202: with large amounts of memory. NetBSD works well on systems with
203: comparatively small amounts of memory. So a natural question is how
204: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
205: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
206: if it is reasonable on a system with 4G.
207:
208: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
209: 1T of disk. 32-bit architectures are viewed as too small to run ZFS.
210:
211: Besides RAM, zfs requires that architecture kernel stack size is at
212: least 12KB or more -- some operations cause stack overflow with 8KB
213: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
214: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
215: have 12KB kernel stack. All others use only 8KB stack, which is not
216: enough to run zfs.
217:
218: NetBSD has many statistics provided via sysctl; see "sysctl
219: kstat.zfs".
220:
221: FreeBSD has tunables that NetBSD does not seem to have, described in
222: [FreeBSD Handbook ZFS Advanced
223: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
224:
225: # Interoperability with other systems
226:
227: Modern ZFS uses pool version 5000 and feature flags.
228:
229: It is in general possible to export a pool and them import the pool on
230: some other system, as long as the other system supports all the used
231: features.
232:
233: \todo Explain how to do this and what is known to work.
234:
235: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
236: macOS.
237:
238: # Sources of ZFS code
239:
240: Currently, there are multiple ZFS projects and codebases:
241:
242: - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
243: - [openzfs repository](https://github.com/openzfs/zfs)
244: - [zfsonlinux](https://zfsonlinux.org/)
245: - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
246: - proprietary ZFS in Solaris (not relevant in open source)
247: - ZFS as released under the CDDL (common ancestor, now of historical interest)
248:
249: OpenZFS is a coordinating project to align open ZFS codebases. There
250: is a notion of a shared core codebase and OS-specific adaptation code.
251:
252: - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
253: - FreeBSD more or less imports code from openzfs and pushes back fixes. \todo Verify this.
254: - NetBSD has imported code from FreeBSD.
255: - The status of ZFS on macOS is unclear (2021-02).
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