I just set up a server with Nexenta Community Edition. Free for 18tb of storage. My system is:
Dual Xeon 2.8Ghz
16Gig Ram
1.5TB HD x 8
Dual GigE
Adaptec Raid 5805 Controller, used as Sata controller only, NO RAID, each drive shows as separate volume for Nexenta to manage.
I went with the Nexenta for two reasons:
1. Inline Deduplication
2. ZFS setup with Raidz-2 for dual drive failure without loosing data.
I am demoting my Drobo from primary storage to backup storage, as it only has single disk failure without loosing data.
With DeDupe on I am getting write speed in the 40-60MB a sec range. Not quite as good as with the Adaptec in Raid 6 mode, but the dedup is very much worth it. My USB drobo was giving me the occasional transfer error, and corrupting my data. I did a verified copy onto the Nexenta and with ZFS end to end checking of CRC's and monthly error check and correction I HOPE to stop bit rot. With a 8TB data store, across 80gig drives to 2tb drives of various ages, it was time to consolidate, error check and correct. Just my 2 cents as I outgrew my drobo.