Re: Amiga RDB partition support for disks >= 2 TB

From: Martin Steigerwald <martin@lichtvoll.de>
To: Martin Steigerwald <martin@lichtvoll.de>
Cc: jdow <jdow@earthlink.net>, Michael Schmitz <schmitzmic@gmail.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Matthew Wilcox <willy@infradead.org>,
	David Sterba <dsterba@suse.cz>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>
Subject: Re: Amiga RDB partition support for disks >= 2 TB
Date: Thu, 28 Jun 2018 13:38:09 +0200	[thread overview]
Message-ID: <51008870.LIDn3ZZdjm@merkaba> (raw)
In-Reply-To: <4710936.m2SbBcP6dP@merkaba>

Martin Steigerwald - 28.06.18, 13:30:
> jdow - 28.06.18, 12:00:
> > On 20180628 01:16, Martin Steigerwald wrote:
> […]
> 
> > >> That brings to the fore an interesting question. Why bother with
> > >> RDBs
> > >> over 2TB unless you want a disk with one single partition? This
> > >> Win10
> > >> monster I am using has a modest BIOS driver partition for the OS
> > >> and
> > >> a giant data partition. That smaller partition would easily work
> > >> with
> > >> any RDB/Filesystem combination since 2.0. So there are some good
> > >> workarounds that are probably "safer" and at least as flexible as
> > >> RDBs, one Linux has used for a very long time, too.
> > > 
> > > Well, my use case was simple:
> > > 
> > > I had this 2 TB disk and I choose to share it as a backup disk for
> > > Linux *and* AmigaOS 4.x on that Sam440ep I still have next to me
> > > desk here.
> > 
> > EEEEEEK! The hair on my neck is standing up straight! Have you heard
> > of SAMBA? The linux mail server firewall etc machine has an extra
> > 4TB
> > disk on it as a backup for the other systems, although a piddly 4TB
> > is small when I save the entire 3G RAID system I have. It's a proof
> > of concept so.... A full backup on a 1gig Ethernet still takes a
> > looooong time. But backing up even an 18GB disk on an Amiga via
> > 100Base-t isn't too bad. And disk speeds of the era being what they
> > were it's about all you can do anyway.
> 
> Heh, the thing worked just fine in Amiga OS 4. I got away with it
> without an issue, until I plugged the disk to my Linux laptop and
> wrote data onto the Linux file system. Mind you, I think in that
> partition marked LNX\0 I even created a Linux LVM with pvcreate. Do
> you call that insane? Well it probably is. :)
> 
> And as an Amiga user I could just return to you: I clicked it, it did
> not warn, so all is good :)
> 
> But yeah, as mentioned I researched the topic before. And I think
> there
> has not even been an overflow within the RDB:
> > The raw, theoretical limit on the maximum device capacity is about
> > 2^105 bytes:
> > 
> > 32 bit rdb_Cylinders * 32 bit rdb_Heads * 32 bit rdb_Sectors * 512
> > bytes/sector for the HD size in struct RigidDiskBlock\0
> 
> http://wiki.amigaos.net/wiki/RDB_(Amiga_Rigid_Disk_Block)
> 
> Confirmed by:
> 
> The .ADF (Amiga Disk File) format FAQ:
> http://lclevy.free.fr/adflib/adf_info.html#p6
> 
> But what do I write, you know the RDB format :)
> 
> So just do the calculation in 96 Bit and you all are set :)

For sectors.

Or

3*32+9 (for 512 bytes per sector) = 105 bits

for bytes.

> Now that is a reason for 128 Bit CPUs :).
> 
> Muuhahaha.
-- 
Martin