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zfs: Note that current mounts zfs first

    1: # ZFS on NetBSD
    2: 
    3: This page attempts to do two things: provide enough orientatino and
    4: pointers to standard ZFS documentation for NetBSD users who are new to
    5: ZFS, and to 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: [Oracle ZFS Administration Manual](https://docs.oracle.com/cd/E26505_01/html/E37384/index.html)
   17: [FreeBSD Handbook ZFS Chapter](https://www.freebsd.org/doc/handbook/zfs.html)
   18: 
   19: # Status of ZFS in NetBSD
   20: 
   21: NetBSD has imported OpenZFS.  \todo versions, links
   22: 
   23: ## NetBSD 8 and earlier
   24: 
   25: While there is some ZFS code, it is old, and seems to have significant
   26: problems.  If one wants to use ZFS, first upgrade to NetBSD 9.  It is
   27: unlikely that anyone is interested in helping, other than telling you
   28: to upgrade to 9.
   29: 
   30: (Reports of how well NetBDS 8 works are welcome on netbsd-users, if it
   31: can actually be recommended for use.)
   32: 
   33: ## NetBSD 9
   34: 
   35: There have been fixes since 9.0 RELEASE.  It is best to upgrade along
   36: the netbsd-9 branch, but the release should be ok.
   37: 
   38: \todo This is OpenZFS as of X.   Most aspects work solidly.
   39: 
   40: \todo This supports pool version 28/5000 (really true?).  Of the
   41: feature flags found in modern OpenZFS, \todo are supported.
   42: 
   43: ## NetBSD current
   44: 
   45: There is initial support for ZFS root, via booting from ffs and pivoting.
   46: 
   47: One can make a ccd using a zvol as a component.  This allows reading a
   48: GPT label from the zvol, which is useful in case the zvol had been
   49: exported via iscsi and some other system created a label.
   50: 
   51: ## things that aren't suported yet
   52: 
   53: \todo (?) hotswap
   54: 
   55: \todo (?) direct boot into zfs root
   56: 
   57: ## Architectures
   58: 
   59: Most people seem to be using amd64.
   60: 
   61: To build zfs, one puts MKZFS=yes in mk.conf.  This is default on amd64
   62: and aarch64 on netbsd-9.  In current, it is also default on sparc64.
   63: 
   64: More or less, zfs can be enabled on an architecture when it is known
   65: to build and run reliably.  (Of course, users are welcome to build it
   66: and report.)
   67: 
   68: # NetBSD-specific information
   69: 
   70: ## rc.conf
   71: 
   72: The main configuration is to put zfs=YES in rc.conf, so that the rc.d
   73: scripts bring up ZFS and mount ZFS filesystems.
   74: 
   75: ## mount order
   76: 
   77: NetBSD 9 mounts other filesystems and then ZFS filesystems.  This can
   78: be a problem if /usr/pkgsrc is on ZFS and /usr/pkgsrc/distfiles is on
   79: NFS.  A workaround is to use noauto and do the mounts in
   80: /etc/rc.local.
   81: 
   82: NetBSD current after 20200301 mounts ZFS first. \todo Explain
   83: consequences.
   84: 
   85: ## TRIM
   86: 
   87: There is some notion of TRIM and zfs using it.
   88: 
   89: \todo Explain how this relates to NetBSD.
   90: 
   91: # Memory usage
   92: 
   93: Basically, ZFS uses lots of memory and most people run it on systems
   94: with large amounts of memory.  NetBSD works well on systems with
   95: comparatively small amounts of memory.  So a natural question is how
   96: well ZFS works on one's VAX with 2M of RAM :-)
   97: 
   98: More seriously, one might ask if is reasonable to run ZFS on a RPI3
   99: with 1G of RAM, or even if it is reasonable on a system with 4G.
  100: 
  101: \todo Give ballpark level for minimum sane RAM, and the amount which
  102: is cleanly enough.
  103: 
  104: FreeBSD has some documentation about memory use.  There is a notion of
  105: a minimum of 1G, and using 1G for 1T of storage, and more if
  106: deduplication is enabled.  FreeBSD considers all i386 systems to be
  107: low memory; this appears to be a clue.
  108: 
  109: \todo Explain if the FreeBSD sysctl list applies, or if not what we
  110: should do instead.
  111: 
  112: [FreeBSD low memory documentation](https://www.freebsd.org/doc/handbook/zfs-advanced.html)
  113: 
  114: # Interoperability with other systems
  115: 
  116: \todo Explain pool version and feature flags relationship to FreeBSD,
  117: Linux, OpenIndiana/Illumos/?, and ?
  118: 
  119: