i'm having a strange issue with a new machine I am using.

We have four 2TB drives in a Z1, shared over CIFS. The board interface is SATA2. One day I will get ~50 MB/sec read and write over a GigE LAN. The next I will get 3MB/sec. I can't have a 3 MB/sec NAS. What should I be looking for? There is nothing weird about this setup at all. No dedupe Compression standard. New board RAM and Proc. Single 40 gig IDE drive in syspool. The mainboard's 4 sata inferfaces are for the 4 drive pool.

SUMMARY INFORMATION: DISKS AND VIRTUAL LUNS
All Disks
Disk    Device  Type    Size    Volume  Attach  Model   Blink
c1d0    cmdk0   disk    37.28 GB    syspool ata Unknown 
c2d0    cmdk2   disk    1.82 TB vol.2tb ata Unknown 
c2d1    cmdk3   disk    1.82 TB vol.2tb ata Unknown 
c3d0    cmdk4   disk    1.82 TB vol.2tb ata Unknown 
c3d1    cmdk5   disk    1.82 TB vol.2tb ata Unknown 
c5d1    cmdk9   disk    37.25 GB        ata Unknown 
Live Disks Statistics
Disk    r/s w/s kr/s    kw/s    wait    actv    wsvc_t  asvc_t  %w  %b
c1d0    0.8 16.0    0.4 78.4    0.0 0.1 1.3 3.2 1   5
c2d0    0.8 81.8    3.5 1145.9  0.3 0.6 3.6 7.1 11  39
c2d1    0.8 81.0    3.5 1139.9  0.4 0.9 4.5 11.5    14  79
c3d0    0.8 81.0    3.5 1144.1  0.8 1.0 9.5 12.5    16  81
c3d1    0.8 80.8    3.5 1132.2  0.8 1.1 9.5 13.9    17  90
c5d1    0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0   0
health  ONLINE
info    raidz1 group: 1, devices: 4
name    vol.2tb
size    7.25T
sync    standard