Annotation of wikisrc/zfs.mdwn, revision 1.35
1.1 gdt 1: # ZFS on NetBSD
2:
1.11 gdt 3: This page attempts to do two things: provide enough orientation and
1.13 wiz 4: pointers to standard ZFS documentation for NetBSD users who are new to
1.11 gdt 5: ZFS, and to describe NetBSD-specific ZFS information. It is
1.1 gdt 6: emphatically not a tutorial or an introduction to ZFS.
7:
8: Many things are marked with \todo because they need a better
1.28 gdt 9: explanation, and some have question marks
1.1 gdt 10:
11: # Documentation Pointers
12:
1.34 gdt 13: See the man pages for zfs(8), zpool(8). Also see zdb(8), if only for
14: seeing pool config info when run with no arguments.
1.1 gdt 15:
1.27 gdt 16: - [OpenZFS Documentation](https://openzfs.github.io/openzfs-docs/)
17: - [OpenZFS admin docs index page](https://github.com/openzfs/zfs/wiki/Admin-Documentation)
18: - [FreeBSD Handbook ZFS Chapter](https://www.freebsd.org/doc/handbook/zfs.html)
1.4 gdt 19: - [Oracle ZFS Administration Manual](https://docs.oracle.com/cd/E26505_01/html/E37384/index.html)
1.24 gdt 20: - [Wikipedia](https://en.wikipedia.org/wiki/ZFS)
1.21 gdt 21:
1.1 gdt 22: # Status of ZFS in NetBSD
23:
1.27 gdt 24: ## NetBSD 8
1.23 gdt 25:
1.27 gdt 26: NetBSD 8 has an old version of ZFS, and it is not recommended for use
27: at all. There is no evidence that anyone is interested in helping
28: with ZFS on 8. Those wishing to use ZFS on NetBSD 8 should therefore
29: update to NetBSD 9.
1.1 gdt 30:
31: ## NetBSD 9
32:
1.27 gdt 33: NetBSD-9 has ZFS that is considered to work well. There have been
34: fixes since 9.0_RELEASE. As always, people running NetBSD 9 are
35: likely best served by the most recent version of the netbsd-9 stable
36: branch. As of 2021-02, ZFS in the NetBSD 9.1 release is very close to
37: netbsd-9.
1.1 gdt 38:
1.32 gdt 39: ### Native blocksize
40:
41: ZFS attempts to find out the native blocksize for a disk when using it
42: in a pool; this is almost always 512 or 4096. Somewhere between 9.0
43: and 9.1, at least some disks on some controllers that used to report
44: 512 now report 4096. This provokes a blocksize mismatch warning.
45:
46: Given that the native blocksize of the disk didn't change, and things
47: seemed OK using the 512 emulated blocks, the warning is likely not
48: critical. However, it is also likely that rebuilding the pool with
49: the 4096 blocksize is likely to result in better behavior because ZFS
50: will only try to do 4096-byte writes. \todo Verify this and find the
51: actual change and explain better.
52:
1.27 gdt 53: ## NetBSD-current
1.1 gdt 54:
1.27 gdt 55: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
1.5 gdt 56:
1.9 gdt 57: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
1.5 gdt 58: ffs and pivoting.
1.1 gdt 59:
1.27 gdt 60: ## NetBSD/xen special issues
1.1 gdt 61:
1.27 gdt 62: In NetBSD-9, MAXPHYS is 64KB in most places, but because of xbd(4) it
63: is set to 32KB for XEN kernels. Thus the standard zfs kernel modules
64: do not work under xen. In NetBSD-current, xbd(4) supports 64 KB
65: MAXPHYS and this is no longer an issue.
1.1 gdt 66:
1.27 gdt 67: Xen and zfs on current are reported to work well together, as of 2021-02.
1.1 gdt 68:
69: ## Architectures
70:
71: Most people seem to be using amd64.
72:
73: To build zfs, one puts MKZFS=yes in mk.conf. This is default on amd64
74: and aarch64 on netbsd-9. In current, it is also default on sparc64.
75:
76: More or less, zfs can be enabled on an architecture when it is known
77: to build and run reliably. (Of course, users are welcome to build it
78: and report.)
79:
1.27 gdt 80: # Quick Start
81:
82: See the [FreeBSD Quickstart
83: Guide](https://www.freebsd.org/doc/handbook/zfs-quickstart.html); only
84: the first item is NetBSD specific.
85:
86: - Put zfs=YES in rc.conf.
87:
88: - Create a pool as "zpool create pool1 /dev/dk0".
89:
90: - df and see /pool1
91:
92: - Create a filesystem mounted on /n0 as "zfs create -o
93: mountpoint=/n0 pool1/n0".
94:
95: - Go back and read the documentation and start over.
96:
1.1 gdt 97: # NetBSD-specific information
98:
99: ## rc.conf
100:
101: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
1.13 wiz 102: scripts bring up ZFS and mount ZFS file systems.
1.1 gdt 103:
1.14 gdt 104: ## pool locations
105:
106: One can add disks or parts of disks into pools. Methods of specifying
107: areas to be included include:
108:
1.29 gdt 109: - entire disks (e.g., /dev/wd0d on amd64, or /dev/wd0 which has the same major/minor)
1.14 gdt 110: - disklabel partitions (e.g., /dev/sd0e)
111: - wedges (e.g., /dev/dk0)
112:
1.33 gdt 113: Information about created or imported pools is stored in
114: /etc/zfs/zpool.cache.
115:
116: ## pool importing problems
117:
118: While one can "zpool pool0 /dev/wd0f" and have a working pool, this
119: pool cannot be exported and imported straigthforwardly. "zpool
1.35 ! gdt 120: export" works fine, and deletes zpool.cache. "zpool import", however,
! 121: only looks at entire disks (e.g. /dev/wd0), and might look at slices
! 122: (e.g. /dev/dk0). It does not look at partitions like /dev/wd0f, and
! 123: there is no way on the command line to ask that specific devices be
! 124: examined. Thus, export/import fails for pools with disklabel
! 125: partitions.
1.33 gdt 126:
127: One can make wd0 be a link to wd0f temporarily, and the pool will then
128: be importable. However, "wd0" is stored in zpool.cache and on the
129: next boot that will attempt to be used. This is obviously not a good
130: approach.
131:
132: One an mkdir e.g. /etc/zfs/pool0 and in it have a symlink to
133: /dev/wd0f. Then, zpool import -d /etc/zfs/pool0 will scan
134: /etc/zfs/pool0/wd0f and succeed. The resulting zpool.cache will have
135: that path, but having symlinks in /etc/zfs/POOLNAME seems acceptable.
136:
137: \todo Determine a good fix, perhaps man page changes only, fix it
138: upstream, in curent, and in 9, before removing this discussion.
139:
1.1 gdt 140: ## mount order
141:
1.13 wiz 142: NetBSD 9 mounts other file systems and then ZFS file systems. This can
1.3 gdt 143: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
144: NFS. A workaround is to use noauto and do the mounts in
145: /etc/rc.local.
146:
1.27 gdt 147: NetBSD current after 20200301 mounts ZFS first. The same issues and
148: workarounds apply in different circumstances.
1.1 gdt 149:
1.19 gdt 150: ## NFS
151:
1.31 gdt 152: zfs filesystems can be exported via NFS, simply by placing them in
153: /etc/exports like any other filesystem.
1.27 gdt 154:
1.31 gdt 155: The "zfs share" command adds a line for each filesystem with the
156: sharenfs property set to /etc/zfs/exports, and "zfs unshare" removes
1.33 gdt 157: it. This file is ignored on NetBSD-9 and current before 20210216; on
158: current after 20210216 those filesystems should be exported (assuming
159: NFS is enabled). It does not appear to be possible to set options
160: like maproot and network restrictions via this method.
1.31 gdt 161:
1.33 gdt 162: On current before 20210216, a remote mkdir of a filesystem mounted via
1.31 gdt 163: -maproot=0:10 causes a kernel NULL pointer dereference. This is now
1.33 gdt 164: fixed.
165:
1.14 gdt 166: ## zvol
167:
168: Within a ZFS pool, the standard approach is to have file systems, but
169: one can also create a zvol, which is a block device of a certain size.
170:
171: \todo The zvol will appear as /dev/???? and can be used in many
172: respects like a slice. However, the system will not read disklabels
173: and gpt labels from a zvol; in this respect it is more like a disklabel
174: partition or wedge than a disk drive.
175:
176: \todo Explain that one can export a zvol via iscsi.
177:
178: \todo Explain if one can swap on a zvol.
179:
180: \todo Explain that one can use ccd to create a normal-looking disk
181: from a zvol. This allows reading a GPT label from the zvol, which is
182: useful in case the zvol had been exported via iscsi and some other
183: system created a label.
184:
1.1 gdt 185: # Memory usage
186:
187: Basically, ZFS uses lots of memory and most people run it on systems
188: with large amounts of memory. NetBSD works well on systems with
189: comparatively small amounts of memory. So a natural question is how
1.27 gdt 190: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
191: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
192: if it is reasonable on a system with 4G.
193:
194: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
195: 1T of disk. 32-bit architectures are viewed as too small to run ZFS.
196:
197: Besides RAM, zfs requires that architecture kernel stack size is at
198: least 12KB or more -- some operations cause stack overflow with 8KB
199: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
200: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
201: have 12KB kernel stack. All others use only 8KB stack, which is not
202: enough to run zfs.
203:
204: NetBSD has many statistics provided via sysctl; see "sysctl
205: kstat.zfs".
206:
207: FreeBSD has tunables that NetBSD does not seem to have, described in
208: [FreeBSD Handbook ZFS Advanced
209: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
1.1 gdt 210:
1.27 gdt 211: # Interoperability with other systems
1.1 gdt 212:
1.27 gdt 213: Modern ZFS uses pool version 5000 and feature flags.
1.1 gdt 214:
1.27 gdt 215: It is in general possible to export a pool and them import the pool on
216: some other system, as long as the other system supports all the used
217: features.
1.10 gdt 218:
1.27 gdt 219: \todo Explain how to do this and what is known to work.
1.26 wiki 220:
1.27 gdt 221: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
222: macOS.
1.1 gdt 223:
1.27 gdt 224: # Sources of ZFS code
1.2 gdt 225:
1.27 gdt 226: Currently, there are multiple ZFS projects and codebases:
1.1 gdt 227:
1.27 gdt 228: - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
1.30 wiz 229: - [openzfs repository](https://github.com/openzfs/zfs)
1.27 gdt 230: - [zfsonlinux](https://zfsonlinux.org/)
231: - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
232: - proprietary ZFS in Solaris (not relevant in open source)
233: - ZFS as released under the CDDL (common ancestor, now of historical interest)
1.1 gdt 234:
1.27 gdt 235: OpenZFS is a coordinating project to align open ZFS codebases. There
236: is a notion of a shared core codebase and OS-specific adaptation code.
1.1 gdt 237:
1.27 gdt 238: - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
1.28 gdt 239: - FreeBSD more or less imports code from openzfs and pushes back fixes. \todo Verify this.
240: - NetBSD has imported code from FreeBSD.
241: - The status of ZFS on macOS is unclear (2021-02).
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