XRAID Slow write, but only via LAN

I have a really strange problem with one of our XRAIDS (we have 2)

The system is connected in the following way:

Client--\ Ethernet FC /-- Tape /XRAID1

Client---Switch------------XServe------- SanBox----XRAID2

Client--/ \Promise RAID

When writing to XRAID 1 from one of the clients transfer speeds are really slow (1mb/ sec max).

The strange thing here is that activity monitor shows over 3300 iops /s on the drive of which most are RDMeta according to fs_usage.

A continuous reed of about 13 MB/s is seen on the drive. This happens on both partitions on the xraid1, each having their own fibre channel controller.

When writing to XRAID 2 or PRAID, all write speeds are >40MB/s, and no read activity can be seen in the monitor.

Here comes the strange part, when writing from xserve to xraid 1 directly transfer speeds are high >40MB/s,, and almost no read operation occours.

Here is what i already did :

- Checked Cache settings (both XRAID's have the same settings)

- Checked the cabeling (switched between xraid 1 and 2)

- Disabled spotlight search completely on all drives

- Tried to copy on a windows client

- Tried to copy with afp/smb/cifs

- Checked free room (800gb free of 2.5 tb)

Who can help me with this?