Annotation of wikisrc/zfs.mdwn, revision 1.29

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: 
                     13: See the man pages for zfs(8) and zpool(8).
                     14: 
1.27      gdt        15:   - [OpenZFS Documentation](https://openzfs.github.io/openzfs-docs/)
                     16:   - [OpenZFS admin docs index page](https://github.com/openzfs/zfs/wiki/Admin-Documentation)
                     17:   - [FreeBSD Handbook ZFS Chapter](https://www.freebsd.org/doc/handbook/zfs.html)
1.4       gdt        18:   - [Oracle ZFS Administration Manual](https://docs.oracle.com/cd/E26505_01/html/E37384/index.html)
1.24      gdt        19:   - [Wikipedia](https://en.wikipedia.org/wiki/ZFS)
1.21      gdt        20: 
1.1       gdt        21: # Status of ZFS in NetBSD
                     22: 
1.27      gdt        23: ## NetBSD 8
1.23      gdt        24: 
1.27      gdt        25: NetBSD 8 has an old version of ZFS, and it is not recommended for use
                     26: at all.  There is no evidence that anyone is interested in helping
                     27: with ZFS on 8.  Those wishing to use ZFS on NetBSD 8 should therefore
                     28: update to NetBSD 9.
1.1       gdt        29: 
                     30: ## NetBSD 9
                     31: 
1.27      gdt        32: NetBSD-9 has ZFS that is considered to work well.  There have been
                     33: fixes since 9.0_RELEASE.  As always, people running NetBSD 9 are
                     34: likely best served by the most recent version of the netbsd-9 stable
                     35: branch.  As of 2021-02, ZFS in the NetBSD 9.1 release is very close to
                     36: netbsd-9.
1.1       gdt        37: 
1.27      gdt        38: ## NetBSD-current
1.1       gdt        39: 
1.27      gdt        40: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
1.5       gdt        41: 
1.9       gdt        42: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
1.5       gdt        43: ffs and pivoting.
1.1       gdt        44: 
1.27      gdt        45: ## NetBSD/xen special issues
1.1       gdt        46: 
1.27      gdt        47: In NetBSD-9, MAXPHYS is 64KB in most places, but because of xbd(4) it
                     48: is set to 32KB for XEN kernels.  Thus the standard zfs kernel modules
                     49: do not work under xen.  In NetBSD-current, xbd(4) supports 64 KB
                     50: MAXPHYS and this is no longer an issue.
1.1       gdt        51: 
1.27      gdt        52: Xen and zfs on current are reported to work well together, as of 2021-02.
1.1       gdt        53: 
                     54: ## Architectures
                     55: 
                     56: Most people seem to be using amd64.
                     57: 
                     58: To build zfs, one puts MKZFS=yes in mk.conf.  This is default on amd64
                     59: and aarch64 on netbsd-9.  In current, it is also default on sparc64.
                     60: 
                     61: More or less, zfs can be enabled on an architecture when it is known
                     62: to build and run reliably.  (Of course, users are welcome to build it
                     63: and report.)
                     64: 
1.27      gdt        65: # Quick Start
                     66: 
                     67: See the [FreeBSD Quickstart
                     68: Guide](https://www.freebsd.org/doc/handbook/zfs-quickstart.html); only
                     69: the first item is NetBSD specific.
                     70: 
                     71:   - Put zfs=YES in rc.conf.
                     72: 
                     73:   - Create a pool as "zpool create pool1 /dev/dk0".
                     74: 
                     75:   - df and see /pool1
                     76: 
                     77:   - Create a filesystem mounted on /n0 as "zfs create -o
                     78:     mountpoint=/n0 pool1/n0".
                     79: 
                     80:   - Go back and read the documentation and start over.
                     81: 
1.1       gdt        82: # NetBSD-specific information
                     83: 
                     84: ## rc.conf
                     85: 
                     86: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
1.13      wiz        87: scripts bring up ZFS and mount ZFS file systems.
1.1       gdt        88: 
1.14      gdt        89: ## pool locations
                     90: 
                     91: One can add disks or parts of disks into pools.  Methods of specifying
                     92: areas to be included include:
                     93: 
1.29    ! gdt        94:   - entire disks (e.g., /dev/wd0d on amd64, or /dev/wd0 which has the same major/minor)
1.14      gdt        95:   - disklabel partitions (e.g., /dev/sd0e)
                     96:   - wedges (e.g., /dev/dk0)
                     97: 
1.1       gdt        98: ## mount order
                     99: 
1.13      wiz       100: NetBSD 9 mounts other file systems and then ZFS file systems.  This can
1.3       gdt       101: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
                    102: NFS.  A workaround is to use noauto and do the mounts in
                    103: /etc/rc.local.
                    104: 
1.27      gdt       105: NetBSD current after 20200301 mounts ZFS first.  The same issues and
                    106: workarounds apply in different circumstances.
1.1       gdt       107: 
1.19      gdt       108: ## NFS
                    109: 
1.27      gdt       110: zfs filesystems are reported to be exportable over NFS.
                    111: 
                    112: The "zfs share" command adds a line to /etc/zfs/exports, and "zfs
                    113: unshare" removes it.
1.19      gdt       114: 
1.27      gdt       115: \todo Explain how /etc/zfs/exports is used.
1.19      gdt       116: 
1.20      gdt       117: This is reported to work on 9.0 STABLE, but to cause a panic on
1.25      gdt       118: current (20200302).  See [misc/55042](http://gnats.netbsd.org/55042).
1.20      gdt       119: 
1.14      gdt       120: ## zvol
                    121: 
                    122: Within a ZFS pool, the standard approach is to have file systems, but
                    123: one can also create a zvol, which is a block device of a certain size.
                    124: 
                    125: \todo The zvol will appear as /dev/???? and can be used in many
                    126: respects like a slice.  However, the system will not read disklabels
                    127: and gpt labels from a zvol; in this respect it is more like a disklabel
                    128: partition or wedge than a disk drive.
                    129: 
                    130: \todo Explain that one can export a zvol via iscsi.
                    131: 
                    132: \todo Explain if one can swap on a zvol.
                    133: 
                    134: \todo Explain that one can use ccd to create a normal-looking disk
                    135: from a zvol.  This allows reading a GPT label from the zvol, which is
                    136: useful in case the zvol had been exported via iscsi and some other
                    137: system created a label.
                    138: 
1.1       gdt       139: # Memory usage
                    140: 
                    141: Basically, ZFS uses lots of memory and most people run it on systems
                    142: with large amounts of memory.  NetBSD works well on systems with
                    143: comparatively small amounts of memory.  So a natural question is how
1.27      gdt       144: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
                    145: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
                    146: if it is reasonable on a system with 4G.
                    147: 
                    148: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
                    149: 1T of disk.  32-bit architectures are viewed as too small to run ZFS.
                    150: 
                    151: Besides RAM, zfs requires that architecture kernel stack size is at
                    152: least 12KB or more -- some operations cause stack overflow with 8KB
                    153: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
                    154: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
                    155: have 12KB kernel stack. All others use only 8KB stack, which is not
                    156: enough to run zfs.
                    157: 
                    158: NetBSD has many statistics provided via sysctl; see "sysctl
                    159: kstat.zfs".
                    160: 
                    161: FreeBSD has tunables that NetBSD does not seem to have, described in
                    162: [FreeBSD Handbook ZFS Advanced
                    163: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
1.1       gdt       164: 
1.27      gdt       165: # Interoperability with other systems
1.1       gdt       166: 
1.27      gdt       167: Modern ZFS uses pool version 5000 and feature flags.
1.1       gdt       168: 
1.27      gdt       169: It is in general possible to export a pool and them import the pool on
                    170: some other system, as long as the other system supports all the used
                    171: features.
1.10      gdt       172: 
1.27      gdt       173: \todo Explain how to do this and what is known to work.
1.26      wiki      174: 
1.27      gdt       175: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
                    176: macOS.
1.1       gdt       177: 
1.27      gdt       178: # Sources of ZFS code
1.2       gdt       179: 
1.27      gdt       180: Currently, there are multiple ZFS projects and codebases:
1.1       gdt       181: 
1.27      gdt       182:   - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
                    183:   - [openzfs repository](https://github.com/openzfs/zfs}
                    184:   - [zfsonlinux](https://zfsonlinux.org/)
                    185:   - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
                    186:   - proprietary ZFS in Solaris (not relevant in open source)
                    187:   - ZFS as released under the CDDL (common ancestor, now of historical interest)
1.1       gdt       188: 
1.27      gdt       189: OpenZFS is a coordinating project to align open ZFS codebases.  There
                    190: is a notion of a shared core codebase and OS-specific adaptation code.
1.1       gdt       191: 
1.27      gdt       192:   - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
1.28      gdt       193:   - FreeBSD more or less imports code from openzfs and pushes back fixes. \todo Verify this.
                    194:   - NetBSD has imported code from FreeBSD.
                    195:   - The status of ZFS on macOS is unclear (2021-02).

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