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Date:      Thu, 10 Feb 2000 13:50:04 +0200
From:      Ruslan Ermilov <ru@ucb.crimea.ua>
To:        Micke Josefsson <mj@isy.liu.se>
Cc:        Ernst de Haan <ernst@znerd.demon.nl>, freebsd-questions@FreeBSD.ORG
Subject:   Re: Boot record repair program?
Message-ID:  <20000210135004.A82756@relay.ucb.crimea.ua>
In-Reply-To: <XFMail.000210122931.mj@isy.liu.se>; from Micke Josefsson on Thu, Feb 10, 2000 at 12:29:31PM %2B0100
References:  <38A28D6F.DE8BADDF@znerd.demon.nl> <XFMail.000210122931.mj@isy.liu.se>

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On Thu, Feb 10, 2000 at 12:29:31PM +0100, Micke Josefsson wrote:
> 
> On 10-Feb-00 Ernst de Haan wrote:
> > It was in `compatible' mode, cuz Winblows didn't start up if me 2nd disk
> > was in `dangerously dedicated mode'.
> > 
> > Any help would be greatly appreciated. I'm going to install a new harddisk
> > now and install FreeBSD on that one and then try to copy all data from the
> > old disk to the new. Problem is, I don't know where the partitions start
> >:(
> > 
> > I used to have my partitions like this (for what I recall):
> > 
> > 1st FreeBSD  (about 3 GB)
> > 2nd Linux (about 3 GB?)
> > 3rd Linux swap (about 120 MB)
> > 
> > But this is what FIPS gives me under DOS (i compressed the table):
> > 
> > --------------------
> > Which Drive (1=0x80/2=0x81/_)? 2
> > 
> > Partition table:
> > 
> >  |boot|    Start |      |     End    | Start  |Number of|
> >#|able|Hd Cyl Sec|System|Hd  Cyl  Sec| Sector |Sectors  |  MB
> > -+----+----------+------+------------+--------+---------+----
> > 1|yes | 1 768  63|   FFh|254 1917  63|16711935| 16753663|8180
> > 2| no | 0 894  63|   FFh|254 1807  63|16753663| 16747519|8177
> > 3| no | 0 768  63|   FFh|  0 1792  63|16711935| 16711935|8160
> > 4| no | 0 768  63|   FFh|  0 1792  63|16711935| 16711935|8160
> > 
> > Checking root sector ... 
> > Error: Invalid root sector signature: FF AA
> > --------------------
> > 
> > 
> > This is weird as I dont recall havig _4_ partitions (but it could be I
> > created different partitions for / and /usr (?) ) and the size of the
> > partitions are way out of bounds for my Quantum Fireball 6.4A (6.4 GB)
> > 
> > 
> 
> A partition table always have 4 entries, even if they are not used. (This is
> why the 1st partition in an extended partition is number 5).
> 
> (A dangerously dedicated disk has no partition table at all. The sector used by
> the partition table is used by FreeBSD instead.)
> 
This is not true.  In dedicated mode we have a fake partition table, with
/boot/boot1 in sector 0 instead of standard /boot/mbr code.

> If this is the only partition info you have, you must have messed up your disk
> somehow. It states there is one (1) partition which starts at cylinder 768 and
> goes on till cylinder 1917. And possibly one partition inside this one (does
> not make sense for now).
> 
> If this is the disk which contained the above FreeBSD/Linux/LinuxSwap then
> there should have been more info in this table or in the MasterBootRecord. You
> should have some info where cylindernumber is 0, this is where the 1st
> partition would start.
> 
> The layout you claim should have been something like this:
> 
> FreeBSD 1    0 63 | 254 xx 63 |
> Linux   0 xx+1 63 | 254 yy 63 |
> 
> where xx is cylinder boundary and yy is ending cylinder (which may NOT need to
> be the actually max available cylinders, DOS/FAT-partitions may not be able to
> allocate all). I'm here assuming that 1) you have set up linux and FreeBSD in
> primary partitions and 2) the linux swap is contained within the linux
> partition (dunno if this is the way linux actually does it). 
> 
> 
> If the linux partition is inside an extended partition then the 2nd entry above
> would have been of type EXTENDED and been pointing to yet another partition
> table. This latter table would also have had 4 entries, the 1st specifying the
> size of your linux partition, the 2nd pointing to possibly another extended
> partition. Entries 3 and 4 would have been empty.
> 
> FreeBSD does not install in an extended partition, linux does.
> 
> The usage of the word 'partition' above is in the DOS/FAT-language, a FreeBSD
> buff would have called them slices (slicii?) instead.
> 
> 
> If you don't touch anything and can boot off a boot floppy a friend of mine has
> a little hack to identify zombie partition tables laying around. With this info
> you should be able to make copies of possible partition table candidates and by
> time consuming (I know!) and careful bitfiddling make new partition tables.
> 
> More (all!) info about your drive would also be neccassary to continue. What
> does BIOS see it as (C/H/S)? Have you repartitioned the drive before or are the
> partition tables inserted only once and on a fresh drive? 
> 
> Restoring partition tables is quite fun once you get the hang of it. It's a bit
> like archaeology or decryption, if that's your cup of tea!
> 
> I'd like to hear of any success
> (and good luck!)
> /Micke
> 
> 
> PS. Perhaps you find it easier to start from a clean slate instead of going
> through all this trouble...
> 
> PS2. The discussion above has got nothing at all to do with the partitions
> FreeBSD sets up inside a slice.
> 
> ----------------------------------
> Michael Josefsson, MSEE
> mj@isy.liu.se
> 
> This message was sent by XFMail
> running on FreeBSD 3.1 
> ----------------------------------
> 
> 
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-- 
Ruslan Ermilov		Sysadmin and DBA of the
ru@ucb.crimea.ua	United Commercial Bank,
ru@FreeBSD.org		FreeBSD committer,
+380.652.247.647	Simferopol, Ukraine

http://www.FreeBSD.org	The Power To Serve
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