Drive Expansion Enclosures and Disk Shelves

An expansion enclosure — often called a disk shelf — is a chassis full of drive bays with no compute of its own. It attaches to a controller, a RAID head or a server HBA and presents its drives to that host. When an array runs out of capacity, adding a shelf is usually far cheaper than replacing the head unit.

How they attach

• SAS — the common attachment on modern shelves, usually via SFF-8088 or SFF-8644 external ports. Shelves are frequently daisy-chained, and the controller sets how many can be chained.
• Fibre Channel — found on the older enterprise arrays, typically 2Gb or 4Gb, and still in service where an FC fabric already exists.

The attachment is not interchangeable. A SAS shelf cannot be presented to an FC controller, and vice versa, regardless of the drives inside.

Bay counts in stock

The common configurations we hold are 12-bay and 24-bay 3.5-inch and 2.5-inch shelves, with 15-bay and 16-bay units from the Fibre Channel era. Bay count is the first thing to match, because it determines both the rack units consumed and the drive carriers required.

Carriers are the part people forget

A shelf takes drives in carriers specific to that enclosure family. A bare drive will not seat, and a carrier from a different vendor or generation usually will not either. Budget for carriers unless the shelf is supplied populated — see our drive caddies and trays.

Firmware and controller pairing

Enclosures report themselves to the controller through SES, and a controller will generally only manage shelves it recognises. Pairing a shelf with a controller from a different family is the most common reason a physically-connected enclosure never appears.

Tell us the controller or array head you are expanding and we will match the shelf, the attachment type and the carriers together rather than leaving the pairing to chance.