Sorry for top-posting, but please: Disk sectors start with 1 (unless you are reformatting the entire track and something like Write Record zero still exists) On DOS-FORMATTED disks, the initial sector is at cylinder 0, head 0, sector 1, and contains within the bootstrap loader what DOS and Windows calls a Partition Table. The rest of track 0 is empty, unless you are running a boot sector virus or such.
-----Original Message----- From: owner-m...@openbsd.org [mailto:owner-m...@openbsd.org] On Behalf Of Kenneth R Westerback Sent: Friday, October 30, 2009 5:38 PM To: Josh Grosse Cc: Amarendra Godbole; misc Subject: Re: Partitioning an external USB drive through OpenBSD -- disklabel On Fri, Oct 30, 2009 at 08:53:45AM -0500, Josh Grosse wrote: > On Fri, 30 Oct 2009 18:44:08 +0530, Amarendra Godbole wrote > > > Thank you all for responses -- I have a better idea now. The only > > thing that I noticed was newfs_msdos wipes out the entire disklabel > > as well as any fdisk created partitions and gobbles up the entire disk. > > > > I guess what James Hartley said in this thread is correct -- Windows > > must be used to create the DOS partition, and then disklabel to get > > the OpenBSD one. > > No, the reason the MBR and disklabel were wiped out was due to an error you > made: starting the partition at sector #0. That sector contians the MBR and > the MBR primary partition table, and the OpenBSD disklabel follows behind. > > Normally, one would begin the first partition -after- the first track > (typically sectors 0-62). > > But, If you were to use Windows disk management to create a FAT partition of > some size on the disk, Windows will begin it at sector #63 for you. Knowledge > of disk geometry and usage is not required by a Windows user, as the tools do > not allow you the control that fdisk(8) does. On MBR formatted disks, sector 0 is the MBR. So overwriting that will indeed toast important information about the disk. However the OpenBSD disklabel is not written to the sector after the MBR if there is an OpenBSD partition, it is written to the second sector of the first OpenBSD partition. So whacking the MSDOS partition starting at sector 0 toasts the MBR, which means the OpenBSD partition cannot be found, which means the disklabel is inaccessable. If you were to re-create the MBR with the correct partitions, the disklabel would re-appear. The MSDOS parition would now be broken of course. :-). As an example here is one of my disks, and a hexdump of the first 65 sectors. The MBR can be seen at sector 0, and the disklabel at sector 64. (64*512 = 32768 = 0x8000). You'll have to take my word I did dd if=/dev/rsd0c of=~/tmp/sect0to64 bs=512 count=65 hexdump -C ~/tmp/sect0to64 > ~/tmp/sect0to64.txt .... Ken Script started on Fri Oct 30 18:11:16 2009 # fdisk sd0 Disk: sd0 geometry: 38913/255/63 [625142448 Sectors] Offset: 0 Signature: 0xAA55 Starting Ending LBA Info: #: id C H S - C H S [ start: size ] ----------------------------------------------------------------------------- -- 0: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused 1: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused 2: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused *3: A6 0 1 1 - 38912 254 63 [ 63: 625137282 ] OpenBSD # disklabel sd0 # /dev/rsd0c: type: SCSI disk: SCSI disk label: WDC WD3200AAKS-0 flags: bytes/sector: 512 sectors/track: 63 tracks/cylinder: 255 sectors/cylinder: 16065 cylinders: 38913 total sectors: 625142448 rpm: 3600 interleave: 1 boundstart: 63 boundend: 625137345 drivedata: 0 16 partitions: # size offset fstype [fsize bsize cpg] a: 417627 63 4.2BSD 2048 16384 1 # / b: 25173855 417690 swap c: 625142448 0 unused d: 417690 25591545 4.2BSD 2048 16384 1 # /tmp e: 417690 26009235 4.2BSD 2048 16384 1 # /var g: 20980890 26426925 4.2BSD 2048 16384 1 # /usr h: 514786860 110350485 4.2BSD 2048 16384 1 # /home i: 20980890 47407815 4.2BSD 2048 16384 1 # /usr/src j: 20980890 68388705 4.2BSD 2048 16384 1 # /usr/ports k: 20980890 89369595 4.2BSD 2048 16384 1 # /usr/xenocara # cat sect0to64.txt 00000000 ea 05 00 c0 07 8c c8 8e d0 bc fc ff 8e d8 b8 a0 |j...@..h.p<|.X8 | 00000010 07 8e c0 31 f6 31 ff b9 00 02 fc f3 a4 ea 22 00 |....@1v19..|s$j".| 00000020 a0 07 1e 07 0e 1f b4 02 cd 16 a8 03 74 0a b0 07 | .....4.M.(.t.0.| 00000030 e8 cb 00 80 0e b4 01 01 f6 c2 80 75 08 be 36 01 |hK...4..vB.u.>6.| 00000040 e8 af 00 b2 80 be be 01 b9 04 00 8a 04 3c 80 74 |h/.2.>>.9....<.t| 00000050 0f 83 c6 10 e2 f5 be 6a 01 e8 96 00 fb f4 eb fc |..F.bu>j.h..{tk|| 00000060 88 d0 24 0f 04 30 a2 27 01 b0 34 28 c8 a2 34 01 |.P$..0"'.04(H"4.| 00000070 56 be 1a 01 f6 06 b4 01 01 75 01 46 e8 73 00 5e |V>..v.4..u.Fhs.^| 00000080 26 c7 06 fe 01 00 00 f6 06 b4 01 01 75 31 88 14 |&G.~...v.4..u1..| 00000090 bb aa 55 b4 41 cd 13 8a 14 72 24 81 fb 55 aa 75 |;*U4AM...r$.{U*u| 000000a0 1e f6 c1 01 74 19 b0 2e e8 53 00 66 8b 4c 08 66 |.vA.t.0.hS.f.L.f| 000000b0 89 0e 12 01 56 b4 42 be 0a 01 cd 13 5e 73 19 b0 |....V4B>..M.^s.0| 000000c0 3b e8 3a 00 8a 74 01 8b 4c 02 b8 01 02 31 db cd |;h:..t..L.8..1[M| 000000d0 13 73 05 be 52 01 eb 81 be 7d 01 e8 14 00 26 81 |.s.>R.k.>}.h..&.| 000000e0 3e fe 01 55 aa 75 05 ea 00 7c 00 00 be 61 01 e9 |>~.U*u.j.|..>a.i| 000000f0 67 ff 50 fc ac 84 c0 74 0f e8 02 00 eb f6 50 53 |gP|,....@t.h..kvps| 00000100 b4 0e bb 01 00 cd 10 5b 58 c3 10 00 01 00 00 00 |4.;..M.[XC......| 00000110 c0 07 00 00 00 00 00 00 00 00 21 55 73 69 6e 67 |@.........!Using| 00000120 20 64 72 69 76 65 20 58 2c 20 70 61 72 74 69 74 | drive X, partit| 00000130 69 6f 6e 20 59 00 4d 42 52 20 6f 6e 20 66 6c 6f |ion Y.MBR on flo| 00000140 70 70 79 20 6f 72 20 6f 6c 64 20 42 49 4f 53 0d |ppy or old BIOS.| 00000150 0a 00 0d 0a 52 65 61 64 20 65 72 72 6f 72 0d 0a |....Read error..| 00000160 00 4e 6f 20 4f 2f 53 0d 0a 00 4e 6f 20 61 63 74 |.No O/S...No act| 00000170 69 76 65 20 70 61 72 74 69 74 69 6f 6e 0d 0a 00 |ive partition...| 00000180 90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 000001b0 00 00 00 00 00 00 4f 78 00 00 00 00 00 00 00 00 |......Ox........| 000001c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 000001e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80 01 |................| 000001f0 01 00 a6 fe ff ff 3f 00 00 00 82 d6 42 25 55 aa |..&~?....VB%U*| 00000200 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00007e00 eb 3c 90 4f 70 65 6e 42 53 44 00 00 02 02 00 00 |k<.OpenBSD......| 00007e10 00 00 00 00 00 f8 00 00 00 00 00 00 10 00 00 00 |.....x..........| 00007e20 00 00 00 00 00 00 29 00 00 00 00 55 4e 49 58 20 |......)....UNIX | 00007e30 4c 41 42 45 4c 55 46 53 20 34 2e 34 00 00 ea 48 |LABELUFS 4.4..jH| 00007e40 00 c0 07 b0 58 e9 37 01 31 c0 8e d0 bc fc 7b 0e |....@.0xi7.1@.P<|{.| 00007e50 1f be e4 01 88 d6 b4 02 cd 16 0c 00 a8 03 74 03 |.>d..V4.M...(.t.| 00007e60 4e 30 f6 e8 56 01 f6 c6 80 74 1e 52 bb aa 55 b4 |N0vhV.vF.t.R;*U4| 00007e70 41 cd 13 5a 72 13 81 fb 55 aa 75 0d f6 c1 01 74 |AM.Zr..{U*u.vA.t| 00007e80 08 c7 06 d1 01 84 01 eb 1a 52 b4 08 cd 13 72 b3 |.G.Q...k.R4.M.r3| 00007e90 88 36 55 01 80 e1 3f 74 aa 88 0e 4c 01 b0 3b e8 |.6U..a?t*..L.0;h| 00007ea0 25 01 5a 66 b8 18 00 00 00 bb e0 07 ff 16 d1 01 |%.Zf8....;`..Q.| 00007eb0 66 be 28 08 00 00 bf 03 00 89 f9 83 f9 0c 72 03 |f>(...?...y.y.r.| 00007ec0 b9 0c 00 bb 00 40 b0 2e e8 fc 00 fc 66 ad 66 60 |9..;....@0.h|.|f-f`| 00007ed0 ff 16 d1 01 66 61 81 c3 00 04 4f e2 e9 09 ff 74 |.Q.fa.C..Obi.t| 00007ee0 22 b8 49 00 08 e4 0f 85 95 00 fe 06 e3 00 66 ad |"8I..d....~.c.f-| 00007ef0 53 bb e0 07 ff 16 d1 01 5b 66 be 00 02 00 00 89 |S;`..Q.[f>.....| 00007f00 f9 eb c3 be f3 01 e8 b3 00 b8 00 40 8e c0 26 81 |ykC>s.h3...@.@&.| 00007f10 3e 02 00 4c 46 74 0f b0 4d be ee 01 a2 f2 01 e8 |>..LFt.0M>n."r.h| 00007f20 9a 00 fb f4 eb fc 51 88 d1 51 66 68 0d d0 01 c0 |..{tk|Q.QQfh.P.@| 00007f30 ea 00 00 12 40 e8 5d 00 66 a1 db 01 8b 0e d5 01 |j...@h].f
