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Re: Beating a dead horse

    Date:        Thu, 26 Nov 2015 07:57:30 -0500
    From:        Greg Troxel <>
    Message-ID:  <>

  | I think 4KB is not because it's the smallest that's workable efficiency
  | wise, but because there is a fragsize which is blocksize/8, and a single
  | 512B sector is the smallest fragment.

Not quite, and that could not be the reason anyway, nothing says that you
must have 8 frags/block, you can have just 2, so with a 512 byte sector
as the smallest fragment (ignoring drives with smaller sector sizes - I
started out in unix using drives that had 256 byte sectors, the driver just
grouped them in units of 2...)

Back in late 1990, early 1991, I was reviewing a draft copy of what became
the answer book to the 4.3BSD design & implementation book (that book had
questions at the end of each chapter, but no answers... the answer book
filled in the gap).

One of the questions related to the minimum block size permitted, to which
the answer in the draft answer book was 4096.   My comment was that I didn't
think that was right, for just the reason I give above.

Kirk Mckusick's reply to that was ...

 | The minimum filesystem blocksize is 4096. This decision was made to ensure
 | that only double indirect blocks would be needed, and to ensure that cylinder
 | groups would be big enough to be useful (since they are by definition, 1
 | block in size). 

I am bcc'ing Kirk in this message, so if he wants to submit a revised
opinion, or something he can - bcc so he doesn't get drawn into the rest
of this (wildly drifting) thread about dead bovines...

Kirk, feel free to reply to me to be forwarded if you have anything to say
on this issue - no need if the above quote from your message of 7 Jan 1991
remains accurate...


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