While full dump(8) success, incremental dump(8) seems to refer out of
range disk block.

# /sbin/dump -5 -t -u -f - -b 64 /dev/rwd0i | ...
  [09:28:17 JST] DUMP: Found /dev/rwd0i on /home in /etc/fstab
  [09:28:17 JST] DUMP: Date of this level 5 dump: Thu May  1 09:28:17 2003
  [09:28:17 JST] DUMP: Date of last level 4 dump: Thu May  1 03:11:30 2003
  [09:28:17 JST] DUMP: Dumping /dev/rwd0i (/home) to standard output
  [09:28:17 JST] DUMP: Label: none
  [09:28:17 JST] DUMP: mapping (Pass I) [regular files]
  [09:28:24 JST] DUMP: mapping (Pass II) [directories]
  [09:30:43 JST] DUMP: readBlocks: read fails: Invalid argument
  [09:30:43 JST] DUMP: read error from /dev/rwd0i: Invalid argument: [block -6593539068]: count=16384
  [09:30:43 JST] DUMP: read error from /dev/rwd0i: Invalid argument: [sector -6593539068]: count=512
  [09:30:43 JST] DUMP: read error from /dev/rwd0i: Invalid argument: [sector -6593539067]: count=512
...

/var/log/message contains error:

May  1 09:28:35 edge /netbsd: pciide0:0: unable to load xfer table DMA map for drive 0, error=22
May  1 09:28:47 edge /netbsd: wd0i: DMA error reading fsbn 12868111936 (wd0 bn 12933593632; cn 12830946 tn 1 sn 1), retrying

"fsck -f" solve this problem?

taca@edge[158]:uname -av
NetBSD edge.back-street.net 1.6R NetBSD 1.6R (CF-R1) #13: Mon Apr 28 01:37:27 JST 2003  taca@edge.back-street.net:/var/obj/sys/arch/i386/compile.i386/CF-R1 i386
taca@edge[159]:ident /netbsd |egrep ffs_v\|ufs_v
     $NetBSD: ffs_vfsops.c,v 1.113 2003/04/16 21:44:27 christos Exp $
     $NetBSD: ffs_vnops.c,v 1.57 2003/04/16 07:38:25 fvdl Exp $
     $NetBSD: ufs_vfsops.c,v 1.14 2003/04/02 10:39:45 fvdl Exp $
     $NetBSD: ufs_vnops.c,v 1.97 2003/04/25 23:12:33 fvdl Exp $
taca@edge[160]:ident /sbin/dump
/sbin/dump:
     $NetBSD: crt0.c,v 1.12 2001/12/30 23:23:38 thorpej Exp $
     $NetBSD: itime.c,v 1.14 2002/11/16 14:15:35 itojun Exp $
     $NetBSD: main.c,v 1.55 2003/04/02 10:39:24 fvdl Exp $
     $NetBSD: optr.c,v 1.30 2003/04/02 10:39:24 fvdl Exp $
     $NetBSD: dumprmt.c,v 1.29 2001/12/25 12:06:26 lukem Exp $
     $NetBSD: rcache.c,v 1.20 2003/04/19 23:29:12 tls Exp $
     $NetBSD: tape.c,v 1.40 2003/04/02 10:39:24 fvdl Exp $
     $NetBSD: traverse.c,v 1.39 2003/04/08 10:02:23 fvdl Exp $
     $NetBSD: unctime.c,v 1.14 2003/04/02 10:39:25 fvdl Exp $
     $NetBSD: ffs_inode.c,v 1.12 2003/04/02 10:39:24 fvdl Exp $
     $NetBSD: ffs_bswap.c,v 1.20 2003/04/16 14:20:25 yamt Exp $

-- 
Takahiro Kambe <taca@back-street.net>