Re: blocksizes

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

    Date:        Fri, 22 Jan 2010 05:46:31 +0000
    From:        David Holland <dholland-tech%NetBSD.org@localhost>
    Message-ID:  <20100122054631.GC23624%netbsd.org@localhost>

  | Since in practice nothing can be larger than the maximum value of
  | off_t anyway, and all counts should be getting carried around as
  | 64-bit values, using byte counts instead of block counts does not
  | change the maximum addressable size of anything and therefore has no
  | particular downside.

One place where that's currently not true is in the quote files,
there block counts are in blocks, and are 32 bits - making the counts
64 bits would double the size of the quota files (the entries really
want to remain a power of two bytes big), and halve cache efficiency
when reading them.   What's more, because we never try to squash two
files' data into the same disc sector (however big that is), we would
gain zero by counting bytes rather than blocks (every entry would simply
have N trailing zero bits)

Changing to 64 bit block counters in there only makes sense once we
really start to need to be able to give users quotas of amounts in the
> 2TB size range (which implies having file systems many times that big).

Like most things, there is no universal correct answer here, simply
deciding "always use bytes" because it seems simpler is unlikely to be
the overall best answer.

kre