Re: FFSv1 (UFS1) vs FFSv2 (UFS2)

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Wed, 3 Jul 2019 19:43:20 +0200
    From:        tlaronde%polynum.com@localhost
    Message-ID:  <20190703174320.GA7939%polynum.com@localhost>

  | But if somebody had numbers about tests comparing FFSv1 and FFSv2 and
  | the efficiency (for formatting,

FFSv1 pre-allocates (ie: zeroes) all of the inode blocks that will ever
be inode blocks.   FFSv2 doesn't, it keeps track of which inode blocks
have been initialised, and clears new ones when they're actually needed
(if one is needed, it will be being written to, to store some new inode
data, so aside from the cost of zeroing a block of mem, this is more or
less free - atually cheaper than FFSv1 as there is no need or point in
reading the existing inode block ... but it doesn't happen often so the
operational difference is negligible).

Since an empty FFS filesystem is essentially just super block and backups,
cylinder group headers, and inode blocks, not init'ing the inode blocks
(which are the vast majority of what a FFSv1 init needs to write) saves
lots of newfs time.

kre