Annotation of wikisrc/zfs.mdwn, revision 1.33

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: 
1.32      gdt        38: ### Native blocksize
                     39: 
                     40: ZFS attempts to find out the native blocksize for a disk when using it
                     41: in a pool; this is almost always 512 or 4096.  Somewhere between 9.0
                     42: and 9.1, at least some disks on some controllers that used to report
                     43: 512 now report 4096.  This provokes a blocksize mismatch warning.
                     44: 
                     45: Given that the native blocksize of the disk didn't change, and things
                     46: seemed OK using the 512 emulated blocks, the warning is likely not
                     47: critical.  However, it is also likely that rebuilding the pool with
                     48: the 4096 blocksize is likely to result in better behavior because ZFS
                     49: will only try to do 4096-byte writes.  \todo Verify this and find the
                     50: actual change and explain better.
                     51: 
1.27      gdt        52: ## NetBSD-current
1.1       gdt        53: 
1.27      gdt        54: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
1.5       gdt        55: 
1.9       gdt        56: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
1.5       gdt        57: ffs and pivoting.
1.1       gdt        58: 
1.27      gdt        59: ## NetBSD/xen special issues
1.1       gdt        60: 
1.27      gdt        61: In NetBSD-9, MAXPHYS is 64KB in most places, but because of xbd(4) it
                     62: is set to 32KB for XEN kernels.  Thus the standard zfs kernel modules
                     63: do not work under xen.  In NetBSD-current, xbd(4) supports 64 KB
                     64: MAXPHYS and this is no longer an issue.
1.1       gdt        65: 
1.27      gdt        66: Xen and zfs on current are reported to work well together, as of 2021-02.
1.1       gdt        67: 
                     68: ## Architectures
                     69: 
                     70: Most people seem to be using amd64.
                     71: 
                     72: To build zfs, one puts MKZFS=yes in mk.conf.  This is default on amd64
                     73: and aarch64 on netbsd-9.  In current, it is also default on sparc64.
                     74: 
                     75: More or less, zfs can be enabled on an architecture when it is known
                     76: to build and run reliably.  (Of course, users are welcome to build it
                     77: and report.)
                     78: 
1.27      gdt        79: # Quick Start
                     80: 
                     81: See the [FreeBSD Quickstart
                     82: Guide](https://www.freebsd.org/doc/handbook/zfs-quickstart.html); only
                     83: the first item is NetBSD specific.
                     84: 
                     85:   - Put zfs=YES in rc.conf.
                     86: 
                     87:   - Create a pool as "zpool create pool1 /dev/dk0".
                     88: 
                     89:   - df and see /pool1
                     90: 
                     91:   - Create a filesystem mounted on /n0 as "zfs create -o
                     92:     mountpoint=/n0 pool1/n0".
                     93: 
                     94:   - Go back and read the documentation and start over.
                     95: 
1.1       gdt        96: # NetBSD-specific information
                     97: 
                     98: ## rc.conf
                     99: 
                    100: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
1.13      wiz       101: scripts bring up ZFS and mount ZFS file systems.
1.1       gdt       102: 
1.14      gdt       103: ## pool locations
                    104: 
                    105: One can add disks or parts of disks into pools.  Methods of specifying
                    106: areas to be included include:
                    107: 
1.29      gdt       108:   - entire disks (e.g., /dev/wd0d on amd64, or /dev/wd0 which has the same major/minor)
1.14      gdt       109:   - disklabel partitions (e.g., /dev/sd0e)
                    110:   - wedges (e.g., /dev/dk0)
                    111: 
1.33    ! gdt       112: Information about created or imported pools is stored in
        !           113: /etc/zfs/zpool.cache.
        !           114: 
        !           115: ## pool importing problems
        !           116: 
        !           117: While one can "zpool pool0 /dev/wd0f" and have a working pool, this
        !           118: pool cannot be exported and imported straigthforwardly.  "zpool
        !           119: export" works fine, and deletes zpool.cache.
        !           120: 
        !           121: "zpool import", however, only looks at entire disks (e.g. /dev/wd0),
        !           122: and might look at slices (e.g. /dev/dk0).  It does not look at
        !           123: partitions like /dev/wd0f, and there is no way on the command line to
        !           124: ask that specific devices be examined.  Thus, export/import fails for
        !           125: pools with disklabel partitions.
        !           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: 
1.20      gdt       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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