[hfs-user] Embedded volume..

Entwicklung entwicklung@whengenibk.de
Fri, 22 Feb 2002 15:05:35 +0100


Hello,
     Thanks for replying... was hoping that someone would respond!

        I was referring to the fields:
  UInt16 drEmbedSigWord ;//embedded volume signature - formerly drVCSize
and HFSExtentDescriptor drEmbedSigWord ;//embedded volume location and
size - formerly drVBMCSize and drCtlCSize

I think what you mentioned about Wrappers is relevant to what I wanted to
know though I don't see the purpose of having a HFS+ partition embedded in a
HFS volume (?). Why would anyone want an embedded partition when all data
could be stored in the original HFS partition? I've just set these fields to
0 right now and I fail to see a situation where I (a third-party HFS-volume
developer) would ever need these.
 Any tips?

Regards,
Nandini Hengen

----- Original Message -----
From: "Simon Bazley" <sibaz@sibaz.com>
To: "Entwicklung" <entwicklung@whengenibk.de>
Cc: <hfs-user@lists.mars.org>
Sent: Friday, February 22, 2002 2:51 PM
Subject: Re: [hfs-user] Embedded volume..


> I'm not sure exactly what you're referring to, but heres a few pointers.
>
> The volume is the thing that you mount on your computer which provides
> files.  It represents the single mount point which appears as a disk on
> your computer.
> The HFS Wrapper is a HFS partition consisting of a massive consecutive
> bad block file, which happens to be a HFS+ partition thats embedded in
> the HFS volume.
> The important difference between HFS+ and HFS is that wheras in HFS
> certain files (Device Drivers, Boot System Files, Allocation Bitmap)
> exist at various physical disk locations (sector 0, sector, sector 4
> etc) and the MDB only gives the location to the Catalog and Extent
> files.  Also there are 2 different address spaces, physical (in
> sectors), and logical (in blocks, starting at 0, after the end of the
> volume bitmap, at the location described in the MDB as the start of free
> space).  HFS+ has very little (if any) system files at fixed locations,
> and everything is referred to in the volume descriptor (replaces the
> MDB), in the way the Catalog and Extent files was before.
>
> Hope that explains everything, if not give me the names of the variable
> in the HFS and HFS+ volume descriptors and I'll explain what they mean.
>
> Simon
>
> Entwicklung wrote:
>
> > Hi,   what exactly does the term embedded volume mean? I've noticed
> > that the HFS MDB has some fields related to this but the HFS+ volume
> > header doesn't seem to. I'm not really using these fields but I'd like
> > to know what they're used for in any case. So if anyone could
> > enlighten me I'd appreciate it. Regards,Nandini Hengen
>