freebsd7 - restore from super-block backup not working?

[John]

Hello

After a crash, when I try to mount the (USB-connected) disk, I get this
error:

# fsck /dev/da0
** /dev/da0
Cannot find file system superblock
ioctl (GCINFO): Inappropriate ioctl for device
fsck_ufs: /dev/da0: can't read disk label

So I did a newfs -N to see the superblocks. I really don't want to lose
the data on here if I can help it:

# newfs -N /dev/da0
/dev/da0: 239372.4MB (490234752 sectors) block size 16384, fragment size
2048
        using 1303 cylinder groups of 183.77MB, 11761 blks, 23552 inodes.
super-block backups (for fsck -b #) at:
 160, 376512, 752864, 1129216, 1505568, 1881920, 2258272, 2634624,
3010976, 3387328, 3763680, 4140032, 4516384, 4892736, 5269088,
 5645440, 6021792, 6398144, 6774496, 7150848, 7527200, 7903552, 8279904,
8656256, 9032608, 9408960, 9785312, 10161664, 10538016,
 10914368, 11290720, 11667072, 12043424, 12419776, 12796128, 13172480,
13548832, 13925184, 14301536, 14677888, 15054240, 15430592,
 15806944, 16183296, 16559648, 16936000, 17312352, 17688704, 18065056,
18441408, 18817760, 19194112, 19570464, 19946816, 20323168,

[loads more]

I know that fsck doesn't see -b, so, using fsck_ufs:

fsck_ufs -b 160 /dev/da0
Alternate super block location: 160
** /dev/da0
160 is not a file system superblock

# fsck_ufs -b 376512 /dev/da0
Alternate super block location: 376512
** /dev/da0
376512 is not a file system superblock

# fsck_ufs -b 752864 /dev/da0
Alternate super block location: 752864
** /dev/da0
752864 is not a file system superblock

# fsck_ufs -b 1129216 /dev/da0
Alternate super block location: 1129216
** /dev/da0
1129216 is not a file system superblock

# fsck_ufs -b 1505568 /dev/da0
Alternate super block location: 1505568
** /dev/da0
1505568 is not a file system superblock

# fsck_ufs -b 1881920 /dev/da0
Alternate super block location: 1881920
** /dev/da0
1881920 is not a file system superblock

...so 3 questions really:

1. is there a way to tell which ones are really superblock backups?
There are thousands.

2. if they're not superblock backups, then why does newfs -N say they are?

3. is the disk just hosed?

thanks
-- 
John