Annotation of wikisrc/zfs.mdwn, revision 1.36

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: 
1.36    ! gdt       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: 
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: 
1.1       gdt       141: ## mount order
                    142: 
1.13      wiz       143: NetBSD 9 mounts other file systems and then ZFS file systems.  This can
1.3       gdt       144: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
                    145: NFS.  A workaround is to use noauto and do the mounts in
                    146: /etc/rc.local.
                    147: 
1.27      gdt       148: NetBSD current after 20200301 mounts ZFS first.  The same issues and
                    149: workarounds apply in different circumstances.
1.1       gdt       150: 
1.19      gdt       151: ## NFS
                    152: 
1.31      gdt       153: zfs filesystems can be exported via NFS, simply by placing them in
                    154: /etc/exports like any other filesystem.
1.27      gdt       155: 
1.31      gdt       156: The "zfs share" command adds a line for each filesystem with the
                    157: sharenfs property set to /etc/zfs/exports, and "zfs unshare" removes
1.33      gdt       158: it.  This file is ignored on NetBSD-9 and current before 20210216; on
                    159: current after 20210216 those filesystems should be exported (assuming
                    160: NFS is enabled).  It does not appear to be possible to set options
                    161: like maproot and network restrictions via this method.
1.31      gdt       162: 
1.33      gdt       163: On current before 20210216, a remote mkdir of a filesystem mounted via
1.31      gdt       164: -maproot=0:10 causes a kernel NULL pointer dereference.  This is now
1.33      gdt       165: fixed.
                    166: 
1.14      gdt       167: ## zvol
                    168: 
                    169: Within a ZFS pool, the standard approach is to have file systems, but
                    170: one can also create a zvol, which is a block device of a certain size.
                    171: 
                    172: \todo The zvol will appear as /dev/???? and can be used in many
                    173: respects like a slice.  However, the system will not read disklabels
                    174: and gpt labels from a zvol; in this respect it is more like a disklabel
                    175: partition or wedge than a disk drive.
                    176: 
                    177: \todo Explain that one can export a zvol via iscsi.
                    178: 
                    179: \todo Explain if one can swap on a zvol.
                    180: 
                    181: \todo Explain that one can use ccd to create a normal-looking disk
                    182: from a zvol.  This allows reading a GPT label from the zvol, which is
                    183: useful in case the zvol had been exported via iscsi and some other
                    184: system created a label.
                    185: 
1.1       gdt       186: # Memory usage
                    187: 
                    188: Basically, ZFS uses lots of memory and most people run it on systems
                    189: with large amounts of memory.  NetBSD works well on systems with
                    190: comparatively small amounts of memory.  So a natural question is how
1.27      gdt       191: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
                    192: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
                    193: if it is reasonable on a system with 4G.
                    194: 
                    195: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
                    196: 1T of disk.  32-bit architectures are viewed as too small to run ZFS.
                    197: 
                    198: Besides RAM, zfs requires that architecture kernel stack size is at
                    199: least 12KB or more -- some operations cause stack overflow with 8KB
                    200: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
                    201: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
                    202: have 12KB kernel stack. All others use only 8KB stack, which is not
                    203: enough to run zfs.
                    204: 
                    205: NetBSD has many statistics provided via sysctl; see "sysctl
                    206: kstat.zfs".
                    207: 
                    208: FreeBSD has tunables that NetBSD does not seem to have, described in
                    209: [FreeBSD Handbook ZFS Advanced
                    210: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
1.1       gdt       211: 
1.27      gdt       212: # Interoperability with other systems
1.1       gdt       213: 
1.27      gdt       214: Modern ZFS uses pool version 5000 and feature flags.
1.1       gdt       215: 
1.27      gdt       216: It is in general possible to export a pool and them import the pool on
                    217: some other system, as long as the other system supports all the used
                    218: features.
1.10      gdt       219: 
1.27      gdt       220: \todo Explain how to do this and what is known to work.
1.26      wiki      221: 
1.27      gdt       222: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
                    223: macOS.
1.1       gdt       224: 
1.27      gdt       225: # Sources of ZFS code
1.2       gdt       226: 
1.27      gdt       227: Currently, there are multiple ZFS projects and codebases:
1.1       gdt       228: 
1.27      gdt       229:   - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
1.30      wiz       230:   - [openzfs repository](https://github.com/openzfs/zfs)
1.27      gdt       231:   - [zfsonlinux](https://zfsonlinux.org/)
                    232:   - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
                    233:   - proprietary ZFS in Solaris (not relevant in open source)
                    234:   - ZFS as released under the CDDL (common ancestor, now of historical interest)
1.1       gdt       235: 
1.27      gdt       236: OpenZFS is a coordinating project to align open ZFS codebases.  There
                    237: is a notion of a shared core codebase and OS-specific adaptation code.
1.1       gdt       238: 
1.27      gdt       239:   - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
1.28      gdt       240:   - FreeBSD more or less imports code from openzfs and pushes back fixes. \todo Verify this.
                    241:   - NetBSD has imported code from FreeBSD.
                    242:   - The status of ZFS on macOS is unclear (2021-02).

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