Re: Changed names of logical disks on recent -CURRENT: part of logical disks not accessible now

From: Marcel Moolenaar <xcllnt_at_mac.com>
Date: Sat, 03 Jan 2009 08:30:08 -0800
On Dec 31, 2008, at 7:16 PM, Jos Backus wrote:

> 	Hi Marcel,
>
> On Mon, Dec 29, 2008 at 10:11:03PM -0800, Marcel Moolenaar wrote:
>> I've seen this before: Erase the second sector on your
>> disk. You likely have a stale BSD disklabel there.
>
> Before I start erasing, does this look like something that can be  
> erased
> safely?
>
> lizzy:~# dd if=/dev/ad0 count=1 skip=1 | hexdump -C
> 1+0 records in
> 1+0 records out
> 512 bytes transferred in 0.009828 secs (52096 bytes/sec)
> 00000000  57 45 56 82 00 00 00 00  61 6d 6e 65 73 69 61 63  | 
> WEV.....amnesiac|
> 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> 00000020  00 00 00 00 00 00 00 00  00 02 00 00 3f 00 00 00   
> |............?...|
> 00000030  10 00 00 00 15 ed 12 00  f0 03 00 00 b0 82 85 4a   
> |...............J|
> 00000040  00 00 00 00 00 00 00 00  10 0e 01 00 00 00 00 00   
> |................|
> 00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> *
> 00000080  00 00 00 00 57 45 56 82  a8 07 08 00 00 20 00 00   
> |....WEV...... ..|
> 00000090  00 00 00 00 00 00 20 00  10 00 00 00 00 08 00 00   
> |...... .........|
> 000000a0  07 08 88 6f 00 00 80 00  10 00 20 00 00 00 00 00   
> |...o...... .....|
> 000000b0  01 00 00 00 b0 82 85 4a  00 00 00 00 00 00 00 00   
> |.......J........|
> 000000c0  00 00 00 00 00 00 20 00  10 00 a0 00 00 08 00 00   
> |...... .........|
> 000000d0  07 08 88 6f 00 00 00 04  10 00 c0 00 00 08 00 00   
> |...o............|
> 000000e0  07 08 88 6f a0 82 c5 45  10 00 c0 04 00 08 00 00   
> |...o...E........|
> 000000f0  07 08 88 6f 00 00 00 00  00 00 00 00 00 00 00 00   
> |...o............|
> 00000100  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> *
> 00000200
>
> Or do you mean /dev/ad0s1? (I thought disklabels generally sit  
> inside fdisk
> partitions^Wslices.)
>
> lizzy:~# dd if=/dev/ad0s1 count=1 skip=1 | hexdump -C
> 1+0 records in
> 1+0 records out
> 512 bytes transferred in 0.016460 secs (31105 bytes/sec)
> 00000000  57 45 56 82 00 00 00 00  61 6d 6e 65 73 69 61 63  | 
> WEV.....amnesiac|
> 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> 00000020  00 00 00 00 00 00 00 00  00 02 00 00 3f 00 00 00   
> |............?...|
> 00000030  10 00 00 00 14 ed 12 00  f0 03 00 00 71 82 85 4a   
> |............q..J|
> 00000040  00 00 00 00 00 00 00 00  10 0e 01 00 00 00 00 00   
> |................|
> 00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> *
> 00000080  00 00 00 00 57 45 56 82  68 07 08 00 00 20 00 00   
> |....WEV.h.... ..|
> 00000090  00 00 00 00 00 00 20 00  10 00 00 00 00 08 00 00   
> |...... .........|
> 000000a0  07 08 88 6f 00 00 80 00  10 00 20 00 00 00 00 00   
> |...o...... .....|
> 000000b0  01 00 00 00 71 82 85 4a  00 00 00 00 00 00 00 00   
> |....q..J........|
> 000000c0  00 00 00 00 00 00 20 00  10 00 a0 00 00 08 00 00   
> |...... .........|
> 000000d0  07 08 88 6f 00 00 00 04  10 00 c0 00 00 08 00 00   
> |...o............|
> 000000e0  07 08 88 6f 61 82 c5 45  10 00 c0 04 00 08 00 00   
> |...oa..E........|
> 000000f0  07 08 88 6f 00 00 00 00  00 00 00 00 00 00 00 00   
> |...o............|
> 00000100  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   
> |................|
> 00000110  00 00 00 00 eb 0e 42 54  58 01 02 80 f6 0f 80 06   
> |......BTX.......|
> 00000120  00 20 00 00 fa 31 c0 8e  d0 bc 00 18 8e c0 8e d8  |. ... 
> 1..........|
> 00000130  66 6a 02 66 9d bf 00 5e  b9 00 19 f3 ab bb 22 95  | 
> fj.f...^......".|
> 00000140  b9 10 00 bf 80 00 89 1d  47 47 ab 83 c3 04 e2 f6   
> |........GG......|
> 00000150  bf 00 5e be d2 95 ac 98  91 e3 1d ac 92 ad 93 ad   
> |..^.............|
> 00000160  b6 08 d1 eb 73 0b 89 05  88 75 02 88 55 05 83 c0   
> |....s....u..U...|
> 00000170  04 8d 7d 08 e2 ec eb de  c6 45 05 18 c6 45 08 10   
> |..}......E...E..|
> 00000180  c6 45 66 68 bb 20 28 e8  b8 00 0f 01 1e c6 95 0f  |.Efh.  
> (.........|
> 00000190  01 16 c0 95 0f 20 c0 40  0f 22 c0 ea 8c 90 08 00   
> |..... ._at_."......|
> 000001a0  31 c9 b1 10 8e d1 b1 38  0f 00 d9 ba 00 a0 00 00  | 
> 1......8........|
> 000001b0  36 0f b7 05 13 04 00 00  c1 e0 0a 2d 00 10 00 00  | 
> 6..........-....|
> 000001c0  29 d0 b1 33 51 50 68 02  02 00 00 6a 2b ff 35 0c  |).. 
> 3QPh....j+.5.|
> 000001d0  90 00 00 51 51 51 51 52  b1 07 6a 00 e2 fc 61 07   
> |...QQQQR..j...a.|
> 000001e0  1f 0f a1 0f a9 cf fa bc  00 18 00 00 0f 20 c0 25   
> |............. .%|
> 000001f0  ff ff ff 7f 0f 22 c0 31  c9 0f 22 d9 0f 01 15 c0  |.....". 
> 1..".....|
> 00000200
>
> Thanks and Happy New Year!

Hi Jos,

"dd if=/dev/zero of=/dev/ad0 count=1 oseek=1" is what you
need. As you say, the BSD disklabel lives in the slice,
so the one in sector 1 (counting from 0) is the stale one
and the one preventing you from booting.

Happy New Year to you (and Trish) too,

-- 
Marcel Moolenaar
xcllnt_at_mac.com
Received on Sat Jan 03 2009 - 15:30:11 UTC

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