Is DAS the storage comeback kid?

Striking a note contrary to convergence and shared storage conventional wisdom, LSI is seeing signs of a resurgence in direct-attached storage.

The prevailing idea is that server proliferation and virtualisation in data centres is strengthening the need for consolidated and shared data storage, either network-attched storage (NAS) for files or block-oriented storage area networks (SANs).

LSI's Robin Wagner, senior director for storage in its components division, says that SAS and small form factor drives are beginning to change that. The evidence is anecdotal and based on LSI shipping more than 13 million SAS integrated circuit (ICs) to its customers for use mostly on servers. LSI has also shipped more than five million SAS RAID stacks, MegaRAID, etc, solely for use on servers. It's looking forward to shipping faster 6Gbit/s SAS ICs towards the end of this year.

Harry Mason, LSI's director of industry marketing, said it's not that LSI's server-oriented SAS IC shipments are growing faster than its Engenio SAS controller storage array business into the SAN and NAS markets. They are growing too and there's no evidence that server SAS is replacing networked array SAS.

The scenario that Wagner and Mason are painting is one where virtualised servers, along with blade servers, can now have a lot of direct-attach, fast-access, SAS storage, particularly with 2.5-inch small form factor drives. SAS zoning, which enables the splitting up of a pool of DAS storage and its mapping to applications helps. The SAS-controller storage can be split up and mapped to individual VMs so that there is consolidated storage for the virtual machines.

They say this is an entry-level virtualised and/or bladed server thing. For more substantial server environments, and to support the movement of VMs and their stored data between physical as well as virtual servers then networked storage will be needed. HP, with its LeftHand Networks software, can take grouped servers' DAS and turn it into a SAN which will suit many SMEs. It pushes the crossover point between DAS and networked storage higher. ®