Annotation of wikisrc/zfs.mdwn, revision 1.39

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: # Status of ZFS in NetBSD
                     12: 
1.27      gdt        13: ## NetBSD 8
1.23      gdt        14: 
1.27      gdt        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.
1.1       gdt        19: 
                     20: ## NetBSD 9
                     21: 
1.27      gdt        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.
1.1       gdt        27: 
1.27      gdt        28: ## NetBSD-current
1.1       gdt        29: 
1.27      gdt        30: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
1.5       gdt        31: 
1.9       gdt        32: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
1.5       gdt        33: ffs and pivoting.
1.1       gdt        34: 
1.27      gdt        35: ## NetBSD/xen special issues
1.1       gdt        36: 
1.36      gdt        37: Summary: if you are using NetBSD, xen and zfs, use NetBSD-current.
                     38: 
1.27      gdt        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
1.36      gdt        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.
1.1       gdt        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: 
1.27      gdt        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: 
1.36      gdt        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)
1.27      gdt        83: 
1.1       gdt        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
1.13      wiz        89: scripts bring up ZFS and mount ZFS file systems.
1.1       gdt        90: 
1.14      gdt        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: 
1.29      gdt        96:   - entire disks (e.g., /dev/wd0d on amd64, or /dev/wd0 which has the same major/minor)
1.14      gdt        97:   - disklabel partitions (e.g., /dev/sd0e)
                     98:   - wedges (e.g., /dev/dk0)
                     99: 
1.33      gdt       100: Information about created or imported pools is stored in
                    101: /etc/zfs/zpool.cache.
                    102: 
1.37      gdt       103: ## pool native blocksize mismatch
1.36      gdt       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: 
1.33      gdt       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
1.35      gdt       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.
1.33      gdt       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: 
1.37      gdt       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: 
1.1       gdt       149: ## mount order
                    150: 
1.13      wiz       151: NetBSD 9 mounts other file systems and then ZFS file systems.  This can
1.3       gdt       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: 
1.27      gdt       156: NetBSD current after 20200301 mounts ZFS first.  The same issues and
                    157: workarounds apply in different circumstances.
1.1       gdt       158: 
1.19      gdt       159: ## NFS
                    160: 
1.31      gdt       161: zfs filesystems can be exported via NFS, simply by placing them in
                    162: /etc/exports like any other filesystem.
1.27      gdt       163: 
1.31      gdt       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
1.33      gdt       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.
1.31      gdt       170: 
1.33      gdt       171: On current before 20210216, a remote mkdir of a filesystem mounted via
1.31      gdt       172: -maproot=0:10 causes a kernel NULL pointer dereference.  This is now
1.33      gdt       173: fixed.
                    174: 
1.14      gdt       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: 
1.38      gdt       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
1.39    ! gdt       190: true that NetBSD can't swap on a zvol?  (When using a zvol for swap,
        !           191: standard advice is to avoid the "-s" option which avoids reserving the
        !           192: allocated space.  Standard advice is also to consider using a
        !           193: dedicated pool.)
1.14      gdt       194: 
                    195: \todo Explain that one can export a zvol via iscsi.
                    196: 
1.38      gdt       197: One can use ccd to create a normal-looking disk from a zvol.  This
                    198: allows reading a GPT label from the zvol, which is useful in case the
                    199: zvol had been exported via iscsi and some other system created a
                    200: label.
1.14      gdt       201: 
1.1       gdt       202: # Memory usage
                    203: 
                    204: Basically, ZFS uses lots of memory and most people run it on systems
                    205: with large amounts of memory.  NetBSD works well on systems with
                    206: comparatively small amounts of memory.  So a natural question is how
1.27      gdt       207: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
                    208: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
                    209: if it is reasonable on a system with 4G.
                    210: 
                    211: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
                    212: 1T of disk.  32-bit architectures are viewed as too small to run ZFS.
                    213: 
                    214: Besides RAM, zfs requires that architecture kernel stack size is at
                    215: least 12KB or more -- some operations cause stack overflow with 8KB
                    216: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
                    217: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
                    218: have 12KB kernel stack. All others use only 8KB stack, which is not
                    219: enough to run zfs.
                    220: 
                    221: NetBSD has many statistics provided via sysctl; see "sysctl
                    222: kstat.zfs".
                    223: 
                    224: FreeBSD has tunables that NetBSD does not seem to have, described in
                    225: [FreeBSD Handbook ZFS Advanced
                    226: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
1.1       gdt       227: 
1.27      gdt       228: # Interoperability with other systems
1.1       gdt       229: 
1.27      gdt       230: Modern ZFS uses pool version 5000 and feature flags.
1.1       gdt       231: 
1.27      gdt       232: It is in general possible to export a pool and them import the pool on
                    233: some other system, as long as the other system supports all the used
                    234: features.
1.10      gdt       235: 
1.27      gdt       236: \todo Explain how to do this and what is known to work.
1.26      wiki      237: 
1.27      gdt       238: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
                    239: macOS.
1.1       gdt       240: 
1.27      gdt       241: # Sources of ZFS code
1.2       gdt       242: 
1.27      gdt       243: Currently, there are multiple ZFS projects and codebases:
1.1       gdt       244: 
1.27      gdt       245:   - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
1.30      wiz       246:   - [openzfs repository](https://github.com/openzfs/zfs)
1.27      gdt       247:   - [zfsonlinux](https://zfsonlinux.org/)
                    248:   - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
                    249:   - proprietary ZFS in Solaris (not relevant in open source)
                    250:   - ZFS as released under the CDDL (common ancestor, now of historical interest)
1.1       gdt       251: 
1.27      gdt       252: OpenZFS is a coordinating project to align open ZFS codebases.  There
                    253: is a notion of a shared core codebase and OS-specific adaptation code.
1.1       gdt       254: 
1.27      gdt       255:   - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
1.28      gdt       256:   - FreeBSD more or less imports code from openzfs and pushes back fixes. \todo Verify this.
                    257:   - NetBSD has imported code from FreeBSD.
                    258:   - The status of ZFS on macOS is unclear (2021-02).

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