Text 2806, 65 rader
Skriven 2011-02-19 20:30:01 av Alex Taylor
Ärende: Re: Ubuntu installation modifies the partition table rendering IBM LVM 
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comp.os.linux.setup:7783 comp.os.os2.setup.storage:380
From: "Alex Taylor" <mail.me@reply.to.address>

On Mon, 14 Feb 2011 04:12:50 UTC, Jonathan de Boyne Pollard 
<J.deBoynePollard-newsgroups@NTLWorld.COM> wrote:

> > Maybe it is, but there is demonstrably an existing base of legacy 
> > software that rigidly assumes it. (OS/2 has always been notoriously 
> > strict about this, or at any rate since the Warp 3 days at least.)
> 
> Actually no.  And that's the point.  There's an existing base of 
> software.  (What was the point of the word "legacy" in that sentence?  

Editing error.  Comes of trying to reword the sentence partway through
writing it. :)

> But it's software that *enforces* the restriction, rather than that 
> *assumes* it.  IBM's FDISK, for example, enforces various restrictions, 
> purportedly for the benefit of other operating systems.  But in fact 
> those other operating systems do *not* assume the restrictions being 
> enforced.  FDISK enforces cylinder alignment.  But I cannot recall off 
> the top of my head *any* operating system back as far as DR-DOS 6 that 
> actually *requires* this in order to work.
> 
> FDISK has several wholly unnecessary impositions, and this is one.

Yup.  I ran up against this back in 1997 or so when I first tried to
install Linux and OS/2 (Warp 3, in that instance) along side each other.
I was eventually pointed to using the FDISK from OS/2 2.11, which was
quite happy to work with the Linux-created partition layout.  

I guess my real point was that this problem isn't specific to LVM,
although it's possibly specific to OS/2 in general.


> It's what IBM's LVM is doing that isn't fine.  It's making unwarranted 
> assumptions about where it can just grab an unallocated disc block 
> without explicitly allocating it.  As I noted, other disc management 
> systems *do not do things this way*.  Microsoft's Logical Disk Manager 
> uses a special partition, whose type is "LDM Metadata" (EFI partition 
> type 5808c8aa-7e8f-42e0-85d2-e1e90434cfb3), and puts the metadata 
> there.  The Linux LVM (we are told) stores the metadata within each 
> partition.  There's a reason that the rest of the world doesn't do 
> things the IBM LVM way, and hasn't done for at least a decade now (There 
> is Windows 2000 Server doco that talks about the pitfalls of expecting 
> unallocated areas of the partition table to be usable.), and this 
> experience *is* that reason.  It's a flawed and selfish design and 
> doesn't work.

Begs the question of course... what, if anything, can be done about it?

I suppose some ambitious developer could rewrite LVM, although when IBM
open-sourced it for the Linux people to use, they only seem to have
released half of it: LVM.DLL was open-sourced, but not (AFAIK) OS2DASD.DMD
and OS2LVM.DMD, which AIUI do fairly critical parts of the work...

-- 
Alex Taylor
Fukushima, Japan
http://www.socis.ca/~ataylo00

Please take off hat when replying.

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