Hmm...according to dmesg, the magic number is wrong...
[root@goldmember:/mnt/olddrive/usr] # dmesg
Copyright (c) 1992-2004 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
The Regents of the University of California. All rights reserved.
FreeBSD 4.10-RELEASE #1: Sun Jan 30 18:01:28 CST 2005
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ad0: 152627MB <WDC WD1600JB-00GVA0> [310101/16/63] at ata0-master UDMA66
ad1: 39266MB <IC35L040AVER07-0> [79780/16/63] at ata0-slave UDMA66
acd0: CDROM <FX4824T> at ata1-master PIO4
Mounting root from ufs:/dev/ad0s1a
ext2fs: #ad/0x2000a: wrong magic number 0 (expected 0xef53)
ext2fs: #ad/0x3000a: wrong magic number 0x1e64 (expected 0xef53)
ext2fs: #ad/0x3000a: wrong magic number 0x1e64 (expected 0xef53)
ext2fs: ad1: wrong magic number 0 (expected 0xef53)
ext2fs: #ad/0x2000a: wrong magic number 0 (expected 0xef53)
ext2fs: #ad/0x2000a: wrong magic number 0 (expected 0xef53)
ext2fs: ad1: wrong magic number 0 (expected 0xef53)
ext2fs: #ad/0x20002: wrong magic number 0x8b6 (expected 0xef53)
ext2fs: #ad/0x3000a: wrong magic number 0x1e64 (expected 0xef53)
ext2fs: #ad/0x2000a: wrong magic number 0 (expected 0xef53)
ext2fs: #ad/0x3000a: wrong magic number 0x1e64 (expected 0xef53)