Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!DBNPIB5.BITNET!VORBRUGG
From: VORBRUGG@DBNPIB5.BITNET
Newsgroups: comp.os.vms
Subject: Re: disk cluster sizes
Message-ID: <8805260045.AA12608@ucbvax.Berkeley.EDU>
Date: 26 May 88 00:45:53 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 40
X-Unparsable-Date: Tue, 24-MAY-1988 01:24 GMT + 1:00

Here's the output of the DCl command HELP INITIALIZE DEVICE /CLUSTER:

INITIALIZE

  Device

    /CLUSTER_SIZE

     /CLUSTER_SIZE=n

     Defines, for disk volumes, the minimum allocation  unit,  in  blocks.
      The  maximum  size you can specify for a volume is one-hundredth the
      size of the volume; the minimum size you can specify  is  calculated
      with the formula:


           disk size  (number of blocks)
           ---------
           255*4096


      For Files-11 Structure Level  2  disks,  the  cluster  size  default
      depends on the disk capacity; disks that are 50,000 blocks or larger
      have a default cluster size of 3, while those  smaller  than  50,000
      blocks have a default value of 1.

      For Files-11 Structure Level 1 disks the cluster size must always be
      1.



As you can see, the minimum follows from the fact that the maximum size
of BITMAP.SYS is 255 blocks (probably a byte sized field somewhere for
historical reasons). So, a cluster=2 disk is allowed up to a 2,088,960
block (slightly less than one gigabyte) disk.

And all that can be found on-line on your VAX/VMS system! Now, who just
said something about reading the <what was that word?> manuals???


Jan Vorbrueggen