Poor iSCSI performance, FreeNAS-8.0.1-RC2

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Sep 20, 2011
Hardware : HP Proliant Microserver, 8GB ram, 4 x Seagate Barracuda LP 2TB drives, Samsung 250GB drive.

Software : FreeNAS-8.0.1-RC2 running off a USB stick, standard configuration with SABNZBD, Couchpotato and Sickbeard services running.

A RAIDZ2 volume was created, using the 4 Seagate drives for storage and the Samsung for a cache drive. I then setup a test iSCSI using a 1TB ZFSvol. A windows 7 machine then successfully connects up to the iSCSI share.

I tested the performace by doing a simple file copy, using a 6GB iso file copied onto the nas. Initally, performance was good, starting at 100MB/s but slowly dropping until it reached around 6MB/s. Presumambly the RAM had been filled up by zfs, so I was expecting to see a performance drop, but 6MB/s was too slow to contemplate letting the file copy finish.

A standard CIFS share, again on the same volume, shows a slow but steady 10MB/s copy - in the end, the CIFS share handled the iso file quicker then the iSCSI share.

Any ideas why the iSCSI performance is so slow? Would ZFS cache the incoming data using the cache drive, and is there anyway of confirming that this is working? I need to dig further into ZFS reporting options, but is there anyway of removing and re-adding a cache drive from an existing volume without destroying it?

Many thanks.
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