You can skip HSM in backups under 6.x too-
zimbraBackupSkipHsmBlobs TRUE
From: "Rich Graves" <rgraves@carleton.edu>
To: "zimbra-hied-admins" <zimbra-hied-admins@sfu.ca>
Sent: Thursday, September 1, 2011 8:40:42 PM
Subject: RE: Scheduled Archive or Deletion of Email
Tony, as of ZCS 7, you *can* skip backups of HSM.
Having no backups of anything older than 15 days would be very bad, but for an IL state .edu feeling the squeeze, it's not the worst option. They could run special HSM backups quarterly, perhaps.
I think the cheapest possible storage is a commodity desktop with a mirrored pair of 2TB drives and iSCSI target software such as OpenFiler or FreeNAS.
If you already have FC expertise in house, a higher performing, lower TCO option is a couple of 2-3 year old shelves of hard drives, pulled from someone else's old SAN and sold on eBay. Look for Xiotech; they're all obsolete. Dual-ported 2gb FC should be fine for HSM. Use Linux software RAID.
If you must buy new, Dell introduced some high-capacity SAS-to-(FC or iSCSI) units a couple months ago (3220F maybe?). Nexsan is the Cadillac of low cost, high performance, low-watt, extremely high-density storage. Infortrend is the Pinto of same. There's lots more small and white-box vendors that pack a lot of hard drives into 4U and let you plug iSCSI or FC into the other end, but they tend not to have the Nexsan/Dell level of expertise necessary to handle vibration dampening, power & cooling, etc.