nfs4 mdadm and dmraid raid mount fails with access denied

Binary package hint: mdadm

According to MDADM the problem was diagnosed as the fallback to NFS3 was not happening and was fixed in nfs-utils 1.2.2.

Forcing -o vers=3 on the mount resolved the symptoms but why is NFS4 not working? What kind of performance is lost by using NFSv3 when NFSv4 is installed?

root@datahouse/# mount -t nfs datahouse:/media/raid/test /Volumes/test
mount.nfs: access denied by server while mounting datahouse:/media/raid/test

root@datahouse/# mount -t nfs -o vers=3 datahouse:/media/raid/test /Volumes/test
!SUCCESS!

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: mdadm 2.6.7.1-1ubuntu15 [modified: sbin/mdadm]
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic x86_64
Architecture: amd64
Date: Mon Sep 20 18:41:10 2010
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Alpha amd64 (20100919)
MDadmExamine.dev.sda: Error: command ['/sbin/mdadm', '-E', '/dev/sda'] failed with exit code 1: mdadm: No md superblock detected on /dev/sda.
MDadmExamine.dev.sda1: Error: command ['/sbin/mdadm', '-E', '/dev/sda1'] failed with exit code 1: mdadm: No md superblock detected on /dev/sda1.
MDadmExamine.dev.sda2: Error: command ['/sbin/mdadm', '-E', '/dev/sda2'] failed with exit code 1: mdadm: No md superblock detected on /dev/sda2.
MDadmExamine.dev.sda5: Error: command ['/sbin/mdadm', '-E', '/dev/sda5'] failed with exit code 1: mdadm: No md superblock detected on /dev/sda5.
MDadmExamine.dev.sdb1: Error: command ['/sbin/mdadm', '-E', '/dev/sdb1'] failed with exit code 1: mdadm: No md superblock detected on /dev/sdb1.
MDadmExamine.dev.sdc1: Error: command ['/sbin/mdadm', '-E', '/dev/sdc1'] failed with exit code 1: mdadm: No md superblock detected on /dev/sdc1.
MachineType: Gigabyte Technology Co., Ltd. GA-880GA-UD3H
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.35-22-generic root=UUID=d271ef77-9c24-432b-8387-efacd47b4ad2 ro quiet splash
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcMDstat:
 Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
 md0 : active raid1 sdc[1] sdb[0]
       1953514496 blocks [2/2] [UU]

 unused devices: <none>
SourcePackage: mdadm
dmi.bios.date: 07/28/2010
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: F4
dmi.board.name: GA-880GA-UD3H
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF4:bd07/28/2010:svnGigabyteTechnologyCo.,Ltd.:pnGA-880GA-UD3H:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-880GA-UD3H:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: GA-880GA-UD3H
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
etc.blkid.tab: Error: [Errno 2] No such file or directory: '/etc/blkid.tab'