Mixed-mode disk arrays came a step closer following Emulex's launch of SATA tunnelling over Fibre Channel technology. This enables controllers to support Fibre Channel drives and cheaper Serial ATA (SATA) drives by tunnelling SATA commands through the Fibre Channel network. Currently, costly bridging technology is needed to do this.

Customers with existing Fibre Channel drive infrastructures can incorporate Emulex' SATA tunnelling technology into Fibre Channel I/O controller chips on RAID board or drive enclosures and so link to SATA drives. If the SATA drives are in an Emulex SBOD, (switched bunch of disks) then, the company claimed, the need for bridging products is completely eliminated.

SATA drives are cheaper than Fibre Channel drives. They tend to be used for storage of secondary data. This is still needed online but not as quickly as primary data such as e-business transaction information. Mixed-mode arrays enable one array to carry both types of information and thus save money.

The Emulex technology parallel's HP FATA, Fibre Attached Technology Adapted, drives, which are SATA drives with a Fibre Channel drive controller board rather than a SATA controller board. This enables drive arrays to have shelves of mixed Fibre Channel and SATA drives, cheaper than separate shelves. HP said that, without FATA, mixed mode drive arrays would require bridging and shelves with either Fibre Channel or SATA drives on them; mixed shelves would not be possible.

FATA drives have been developed by HP, Seagate and HDS. HP has an 'exclusivity clause' contract guaranteeing it the first 40,000 FATA drives made, according to Skip Jones, QLogic's director of planning and technology. That's 20,000 from Seagate and 20,000 from HDS. After that Seagate and HDS can sell their FATA drives on the open market.

FATA drives are priced a little higher than SATA drives. With Emulex tunnelling technology, commodity SATA drives can be used and the resulting products could be cheaper than mixed Fibre Channel/FATA arrays. If HP doesn't reach its 40,000 number until 2006/7 then Emulex would have a clear run at the market.

Emulex intends to offer its tunnelling technology as a potential industry standard to the T11 committee. In the meantime, Emulex will demonstrate its technology in April at the Storage Networking World Spring 2005 Conference in Phoenix, Arizona.

SATA tunnelling has been used before
Emulex's use of SATA tunnelling over Fibre Channel follows on from the existing use of SATA tunnelling over serial-attached SCSI (SAS). STP, the SATA Tunneling Protocol, was designed into SAS at its inception and enables an SAS controller to link to SATA drives as well as SAS drives. Several vendors, such as ARIO Data provide products using it.