File:  [NetBSD Developer Wiki] / wikisrc / zfs.mdwn
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zfs: rototill and simplify

    1: # ZFS on NetBSD
    2: 
    3: This page attempts to do two things: provide enough orientation and
    4: pointers to standard ZFS documentation for NetBSD users who are new to
    5: ZFS, and to describe NetBSD-specific ZFS information.  It is
    6: emphatically not a tutorial or an introduction to ZFS.
    7: 
    8: Many things are marked with \todo because they need a better
    9: explanation, and some have question marks, indicating that the
   10: statement needs verification.
   11: 
   12: # Documentation Pointers
   13: 
   14: See the man pages for zfs(8) and zpool(8).
   15: 
   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)
   19:   - [Oracle ZFS Administration Manual](https://docs.oracle.com/cd/E26505_01/html/E37384/index.html)
   20:   - [Wikipedia](https://en.wikipedia.org/wiki/ZFS)
   21: 
   22: # Status of ZFS in NetBSD
   23: 
   24: ## NetBSD 8
   25: 
   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.
   30: 
   31: ## NetBSD 9
   32: 
   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.
   38: 
   39: ## NetBSD-current
   40: 
   41: NetBSD-current (as of 2021-02) has similar ZFS code to 9.
   42: 
   43: There is initial support for [[ZFS root|wiki/RootOnZFS]], via booting from
   44: ffs and pivoting.
   45: 
   46: ## NetBSD/xen special issues
   47: 
   48: In NetBSD-9, MAXPHYS is 64KB in most places, but because of xbd(4) it
   49: is set to 32KB for XEN kernels.  Thus the standard zfs kernel modules
   50: do not work under xen.  In NetBSD-current, xbd(4) supports 64 KB
   51: MAXPHYS and this is no longer an issue.
   52: 
   53: Xen and zfs on current are reported to work well together, as of 2021-02.
   54: 
   55: ## Architectures
   56: 
   57: Most people seem to be using amd64.
   58: 
   59: To build zfs, one puts MKZFS=yes in mk.conf.  This is default on amd64
   60: and aarch64 on netbsd-9.  In current, it is also default on sparc64.
   61: 
   62: More or less, zfs can be enabled on an architecture when it is known
   63: to build and run reliably.  (Of course, users are welcome to build it
   64: and report.)
   65: 
   66: # Quick Start
   67: 
   68: See the [FreeBSD Quickstart
   69: Guide](https://www.freebsd.org/doc/handbook/zfs-quickstart.html); only
   70: the first item is NetBSD specific.
   71: 
   72:   - Put zfs=YES in rc.conf.
   73: 
   74:   - Create a pool as "zpool create pool1 /dev/dk0".
   75: 
   76:   - df and see /pool1
   77: 
   78:   - Create a filesystem mounted on /n0 as "zfs create -o
   79:     mountpoint=/n0 pool1/n0".
   80: 
   81:   - Go back and read the documentation and start over.
   82: 
   83: # NetBSD-specific information
   84: 
   85: ## rc.conf
   86: 
   87: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
   88: scripts bring up ZFS and mount ZFS file systems.
   89: 
   90: ## pool locations
   91: 
   92: One can add disks or parts of disks into pools.  Methods of specifying
   93: areas to be included include:
   94: 
   95:   - entire disks (e.g., /dev/wd0d on amd64)
   96:   - disklabel partitions (e.g., /dev/sd0e)
   97:   - wedges (e.g., /dev/dk0)
   98: 
   99: ## mount order
  100: 
  101: NetBSD 9 mounts other file systems and then ZFS file systems.  This can
  102: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
  103: NFS.  A workaround is to use noauto and do the mounts in
  104: /etc/rc.local.
  105: 
  106: NetBSD current after 20200301 mounts ZFS first.  The same issues and
  107: workarounds apply in different circumstances.
  108: 
  109: ## NFS
  110: 
  111: zfs filesystems are reported to be exportable over NFS.
  112: 
  113: The "zfs share" command adds a line to /etc/zfs/exports, and "zfs
  114: unshare" removes it.
  115: 
  116: \todo Explain how /etc/zfs/exports is used.
  117: 
  118: This is reported to work on 9.0 STABLE, but to cause a panic on
  119: current (20200302).  See [misc/55042](http://gnats.netbsd.org/55042).
  120: 
  121: ## zvol
  122: 
  123: Within a ZFS pool, the standard approach is to have file systems, but
  124: one can also create a zvol, which is a block device of a certain size.
  125: 
  126: \todo The zvol will appear as /dev/???? and can be used in many
  127: respects like a slice.  However, the system will not read disklabels
  128: and gpt labels from a zvol; in this respect it is more like a disklabel
  129: partition or wedge than a disk drive.
  130: 
  131: \todo Explain that one can export a zvol via iscsi.
  132: 
  133: \todo Explain if one can swap on a zvol.
  134: 
  135: \todo Explain that one can use ccd to create a normal-looking disk
  136: from a zvol.  This allows reading a GPT label from the zvol, which is
  137: useful in case the zvol had been exported via iscsi and some other
  138: system created a label.
  139: 
  140: # Memory usage
  141: 
  142: Basically, ZFS uses lots of memory and most people run it on systems
  143: with large amounts of memory.  NetBSD works well on systems with
  144: comparatively small amounts of memory.  So a natural question is how
  145: well ZFS works on one's VAX with 2M of RAM :-) More seriously, one
  146: might ask if it is reasonable to run ZFS on a RPI3 with 1G of RAM, or
  147: if it is reasonable on a system with 4G.
  148: 
  149: The prevailing wisdom is more or less that ZFS consumes 1G plus 1G per
  150: 1T of disk.  32-bit architectures are viewed as too small to run ZFS.
  151: 
  152: Besides RAM, zfs requires that architecture kernel stack size is at
  153: least 12KB or more -- some operations cause stack overflow with 8KB
  154: kernel stack. On NetBSD, the architectures with 16KB kernel stack are
  155: amd64, sparc64, powerpc, and experimental ia64, hppa. mac68k and sh3
  156: have 12KB kernel stack. All others use only 8KB stack, which is not
  157: enough to run zfs.
  158: 
  159: NetBSD has many statistics provided via sysctl; see "sysctl
  160: kstat.zfs".
  161: 
  162: FreeBSD has tunables that NetBSD does not seem to have, described in
  163: [FreeBSD Handbook ZFS Advanced
  164: section](https://docs.freebsd.org/en/books/handbook/zfs/#zfs-advanced).
  165: 
  166: # Interoperability with other systems
  167: 
  168: Modern ZFS uses pool version 5000 and feature flags.
  169: 
  170: It is in general possible to export a pool and them import the pool on
  171: some other system, as long as the other system supports all the used
  172: features.
  173: 
  174: \todo Explain how to do this and what is known to work.
  175: 
  176: \todo Explain feature flags relationship to FreeBSD, Linux, iIllumos,
  177: macOS.
  178: 
  179: # Sources of ZFS code
  180: 
  181: Currently, there are multiple ZFS projects and codebases:
  182: 
  183:   - [OpenZFS](http://www.open-zfs.org/wiki/Main_Page)
  184:   - [openzfs repository](https://github.com/openzfs/zfs}
  185:   - [zfsonlinux](https://zfsonlinux.org/)
  186:   - [OpenZFS on OS X ](https://openzfsonosx.org/) [repo](https://github.com/openzfsonosx)
  187:   - proprietary ZFS in Solaris (not relevant in open source)
  188:   - ZFS as released under the CDDL (common ancestor, now of historical interest)
  189: 
  190: OpenZFS is a coordinating project to align open ZFS codebases.  There
  191: is a notion of a shared core codebase and OS-specific adaptation code.
  192: 
  193:   - [zfsonlinux relationship to OpenZFS](https://github.com/openzfs/zfs/wiki/OpenZFS-Patches)
  194:   - FreeBSD more or less imports code from openzfs and pushes back fixes. \verify
  195:   - NetBSD has imported code from FreeBSD
  196:   - The status of ZFS on macOS is unclear (2021-02)

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