Re: RAID stripe size

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

    Date:        Wed, 30 Apr 2025 09:27:45 +0200
    From:        Edgar Fu�<ef%math.uni-bonn.de@localhost>
    Message-ID:  <aBHQ8WxxEI48Q1/t%trav.math.uni-bonn.de@localhost>

  | > By "fragments in use" do you mean
  | > 
  | > 1) Fragment-sized pieces of disk with file data in them?
  | > 2) Blocks with some but not all fragments occupied?
  | > 3) Files with trailing sub-block portions?
  | > 4) Fragment-sized pieces of disk occupied by (3)?
  | Probably 1.

You probably really meant 4.   Though that depends whether by 4
Mouse meant the extra 1..7 fragment sized bits at the end of the
file (the "trailing sub-block portions") or the total number of
frag sized pieces allocated by files which have trailing sub-block
portions.  That wasn't clear from what was asked, but the former is
what I have been assuming was what you wanted to know (ie: how much
allocated space is in smaller than fs_bsize sized allocations, and so
on a raid with fs_bsize sized stripes how often would a RMW sequence be
needed for writing to a stripe).

1 is just what df tells you (how much space is used in the filesys,
just probably in different units).

kre