review request: 2TB disk limit in disks chapter

[Brooks Davis]

On Mon, Sep 13, 2004 at 10:49:58PM +0200, Simon L. Nielsen wrote:
> On 2004.09.13 13:21:07 -0700, Brooks Davis wrote:
> > People are starting to build disk arrays larger then 2TB and then
> > finding they can't label them.  I'd like to add some text like the
> > following to the handbook section on adding disks.  A table of
> 
> Great, documenting this is very useful!
> 
> > capabilities would probably be useful and could be an intresting project
> > for someone who wanted to do a little research, but I'm specificaly
> > trying to address bsdlabel at this point.
> > 
> > Please review my changes below.
> 
> All the entities should be closed, e.g. "&man.bsdlabel.8" should be
> "&man.bsdlabel.8;".

Doh.

> > Index: chapter.sgml
> > ===================================================================
> > RCS file: /home/dcvs/doc/en_US.ISO8859-1/books/handbook/disks/chapter.sgml,v
> > retrieving revision 1.220
> > diff -u -p -r1.220 chapter.sgml
> > --- chapter.sgml	25 Aug 2004 10:33:59 -0000	1.220
> > +++ chapter.sgml	13 Sep 2004 20:14:19 -0000
> > @@ -202,6 +202,12 @@
> >        case, the drive will be added simply as
> >        <filename>/dev/da1e</filename>.</para>
> >  
> > +    <para>Due to the use of 32-bit integers to store the number of sectors, 
> 
> I think there is trailing whitespace on this line (unless it's just my
> MUA/editor).

Yah, I've fixed that here.

> > +      &man.bsdlabel.8, &man.disklabel.8, &man.fdisk.8, and
> 
> Isn't disklabel just a link to the local label (bsdlabel/sunlabel
> etc.) now?

The rest of the file seems to list both of them and the limitation
applies to 4.x where there is only disklabel.  I don't have a strong
oppinion on this one.

> > +      <application>sunlabel</application> are all limited to 2^32-1
> 
> You should also use a manual page entity for sunlabel.

Fixed.

> > +      sectors.  This usually translates to a 2TB limit on disk size.
> > +      For larger disks, &man.gpt.8 partitions may be used.</para>
> 
> Shouldn't that be "2TB limits on partition size.", since you can AFAIR?
> make multiple <2TB partitions on one "disk"(/RAID)?

It's more complicated then that, which means I need to revise this
documentation.  In bsdlabel, the size of the disk in sectors is also
recorded capping the format at 2TB.  In fdisk, the format appears to
limit the partition size to 2TB and the offset to 2TB so around 4TB.
This doesn't work at the moment because fdisk doesn't correctly use
64-bit types internally. sunlabel appears to allow up to 16TB disks with
2TB partitions.

Here's a new version.

-- Brooks

Index: chapter.sgml
===================================================================
RCS file: /home/dcvs/doc/en_US.ISO8859-1/books/handbook/disks/chapter.sgml,v
retrieving revision 1.220
diff -u -p -r1.220 chapter.sgml
--- chapter.sgml	25 Aug 2004 10:33:59 -0000	1.220
+++ chapter.sgml	13 Sep 2004 21:12:20 -0000
@@ -202,6 +202,15 @@
       case, the drive will be added simply as
       <filename>/dev/da1e</filename>.</para>
 
+    <para>Due to the use of 32-bit integers to store the number of sectors
+      &man.bsdlabel.8; is limited to 2^32-1 sectors per disk or 2TB
+      in most cases.  The &man.fdisk.8; format is allows a starting
+      sector of no more than 2^32-1 and a length of no more than 2^32-1,
+      limiting partitions to 2TB and disks to 4TB in most cases.  The
+      &man.sunlabel.8; format is limited to 2^32-1 sectors per parition
+      and 8 partitions for a total of 16TB. larger disks, &man.gpt.8
+      partitions may be used.</para>
+
     <sect2>
       <title>Using &man.sysinstall.8;</title>
       <indexterm>

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