linux-kernel - Re: Partitions: Amiga RDB partition on 2 TB disk way too big, while OK in AmigaOS 4.1

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Date:	Mon, 18 Jun 2012 23:14:16 +0200
From:	Martin Steigerwald <Martin@...htvoll.de>
To:	jdow <jdow@...thlink.net>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	linux-m68k@...r.kernel.org
Subject: Re: Partitions: Amiga RDB partition on 2 TB disk way too big, while OK in AmigaOS 4.1

Am Sonntag, 17. Juni 2012 schrieb jdow:
> On 2012/06/17 14:06, Martin Steigerwald wrote:
> > Am Sonntag, 17. Juni 2012 schrieb Geert Uytterhoeven:
> >> On Sun, Jun 17, 2012 at 2:58 PM, Martin Steigerwald 
<Martin@...htvoll.de> wrote:
> >>> Am Sonntag, 17. Juni 2012 schrieb jdow:
> >>> | JXFS 64 bit file system
> >>> | 
> >>> | With AmigaOS 4.x a new file system has been introduced called
> >>> | JXFS. It is a totally new 64 bit file system that supports
> >>> | partitions up to 16 TB in size. It is a modern journalling file
> >>> | system, which means that it reduces data loss if data writes to
> >>> | the disk are interrupted. It is the fastest and most reliable
> >>> | file system ever created for AmigaOS.
> >>> 
> >>> http://www.amigaos.net/content/1/features
> >>> 
> >>> Well I asked AmigaOS 4 developers about this issue as well. Lets
> >>> see what they say about 2 TB limits.
> >> 
> >> 16 TB = 2 TB * 8. Perhaps they increased the block size from 512 to
> >> 4096?
> > 
> > I hope to get anything back from the AmigaOS 4 developers.
> > 
> >> block/partitions/amiga.c reads the block size from
> >> RigidDiskBlock.rdb_BlockBytes,
> >> but after conversion to 512-byte blocks, all further calculations
> >> are done on "int", so it will overflow for disks larger than 2 TiB.
> >> 
> >> Note that in your profile-binary.img, the field is 0x200, i.e. 512
> >> bytes per block,
> >> so I'll have to get a deeper look into your RDB first...
> > 
> > Okay, thanks!
> > 
> > I did not get any information regarding the current size limit yet.
> > 
> > Strangely on AmigaOS 4.1 all values seem to be fine except for the
> > total sectors value.
> 
> > And on Linux begin and end cylinders are correct, only size is off:
> Ah, you DO know that "cylinders, surfaces, and tracks" are polite
> fictions in AmigaOS, don't you? Start and End blocks are all that
> matter on a real Amiga. The fictions arose because at first it was
> thought they could be used to optimize disk accesses. Once drives
> were notched these values became meaningless. So they're created on
> the fly picking values out of the nose or something. (RDPrep tries
> to find reasonable size factors for the total block counts.)

I know there are pure fiction on Linux as well. As in any other modern 
operating system.

Actually Media Toolbox shows both. Physical and logical sizes. See the 
screenshots I attached to the bug report.

> > merkaba:~> amiga-fdisk -l /dev/sdb
> 
> Are you sure "amiga-fdisk" is not broken?

Not at all, but there is also the syslog.

> > Disk /dev/sdb: 3 heads, 16 sectors, 81396441 cylinders, RDB: 0
> > Logical Cylinders from 43 to 81396440, 24576  bytes/Cylinder
> > 
> > Device     Boot Mount   Begin      End     Size   Pri  BBlks   
> > System /dev/sdb1       *        43   65536043   1572864024     0    
> >  0  Linux native /dev/sdb2       *    65536044   78643244  
> > 314572824     0      0  [unknown] /dev/sdb3       *    78643245  
> > 81396440   66076704     0      0  Amiga FFS Int.
> > 
> > But not only from the first, also of the second and third one it
> > seems.
> > 
> > 65536043 - 43 = 65536000
> 
> So the size in bytes is 24 times the byte offset of the start of the
> next partition. Fascinating. Let's see. You are working in 512 byte
> blocks it looks like. With RDBs in blocks that means you can get up to
> 1099511627776 bytes, 2147483648 blocks, or 44739242. So you are
> already WAY over what can be expressed in the 32 bit values in the
> RDBs. So the software that prepared your partitioning needs some
> repair work of some sort or something other than traditional Amiga FFS
> format disks.
> 
> The first thing on the agenda is "fixing" the partitioning software. Is
> the version of Amiga FFS you are using cognizant of 64 bit values? If
> not you will have to go to block sizes larger than 512 bytes. It looks
> like 1k is suitable for this instance. Given the way Amiga FFS stores
> data on the disk I'd go for 4k or 8k block sizes unless you have lots
> of very small files.

Is there still something to fix in there? Just still catching up the mail 
exchange. From what I could see on AmigaOS 4.1 all seemed well. I already 
reported the negative sector count value.

Anyway, if there is an issue left we can discuss this privately. This 
would have nothing to do with Linux and I can make sure that current 
AmigaOS developers hear about your oppinion.

Ciao,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7
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