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

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Message-ID: <4710936.m2SbBcP6dP@merkaba>
Date:   Thu, 28 Jun 2018 13:30:35 +0200
From:   Martin Steigerwald <martin@...htvoll.de>
To:     jdow <jdow@...thlink.net>
Cc:     Michael Schmitz <schmitzmic@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Sterba <dsterba@...e.cz>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>
Subject: Re: Amiga RDB partition support for disks >= 2 TB

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.

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 :)

Now that is a reason for 128 Bit CPUs :).

Muuhahaha.

Ciao,
-- 
Martin