NFS Write-Issue??

Hi there,
i've got a 3 head cluster running and a nfs-storage server based on debian squeeze. the Storage ist mounted on the cluster and i 've got some machines running there.

The thing is, when a machine has write transactions i can see in iotop that the transaction is not pushed directly to the nfs-server. its some seconds below. The nfs-server flushes the data and then, silence. in this time the rsync-command doesn't transfer any data since the write-io on the nfs-server is quiet again.

is there something wrong in my configuration?

here's the nfs-part of the storage.cfg
nfs: NFS-Storage0
path /mnt/pve/NFS-Storage0
server 10.1.0.200
export /mnt/drbd
options vers=3
content images,iso,vztmpl,backup
maxfiles 3


i'm running this version of pve:
pveversion -v
pve-manager: 2.2-32 (pve-manager/2.2/3089a616)
running kernel: 2.6.32-17-pve
proxmox-ve-2.6.32: 2.2-83
pve-kernel-2.6.32-17-pve: 2.6.32-83
pve-kernel-2.6.32-16-pve: 2.6.32-82
lvm2: 2.02.95-1pve2
clvm: 2.02.95-1pve2
corosync-pve: 1.4.4-1
openais-pve: 1.1.4-2
libqb: 0.10.1-2
redhat-cluster-pve: 3.1.93-2
resource-agents-pve: 3.9.2-3
fence-agents-pve: 3.1.9-1
pve-cluster: 1.0-34
qemu-server: 2.0-72
pve-firmware: 1.0-21
libpve-common-perl: 1.0-41
libpve-access-control: 1.0-25
libpve-storage-perl: 2.0-36
vncterm: 1.0-3
vzctl: 4.0-1pve2
vzprocps: 2.0.11-2
vzquota: 3.1-1
pve-qemu-kvm: 1.3-10
ksm-control-daemon: 1.1-1



thanks a lot