I am seeing an interesting phenomenon. Freenas runs on a 3GHz CPU as iSCSI target with an extend on a software RAID 5 array. The target is mounted into a Windows 2008 Enterprise Server.
On this Window server I copy from the iSCSI drive to a another Windows network share and I am seeing initially around 350-400 Mbs transfer speeds. This starts to taper off oscillating up and down to rest after 5-10 minutes are at about 160Mbs.
Now when I grab in on the Windows server another file from the iSCSI drive and copy it to local disk in parallel to the copy from iSCSI disk to network share, Freenas blasts out 600Mbs for both copy processes.
When I cancel the “to local disk copy” the transfer speed for the copy from iSCSI to network share jumps up again to 350-400 Mbs and the tapers of again as above to be after 5-10 minutes or so at 160 Mbs,
So something is slowing the data transfer down. This could be on the Windows 2008 Server box or Freenas. I saw some other users complaining about low speed of about the same rate of 160 Mbs.
The Freenas box can read fine at 80>MBs and my network share can write at about 45 MB/s, the local disk at 85>MBs. Something on the network side seems to bring the speed down over time when copying large files, 120 GB or so. I can restart the speed to about 3x by simply putting for a short period of time more load on the Freenas box and the same network connection.
If I copy from a physical drive from the Windows 2008 box to the network share this problem is not apparent. I attach a screenshot from the Win 2008 server box showing the process I described from the network view.
LAN 5 = iSCSI if, LAN 3 = LAN if, on Win2008 Server