How can direct attached storage (DAS) make a comeback if it never left?

Have you seen or heard the theme that Direct Attached Storage (DAS), either dedicated or shared, internal or external is making a comeback?

Wait, if something did not go away, how can it make a comeback?

IMHO it is as simple as for the past decade or so, DAS has been overshadowed by shared networked storage including switched SAS, iSCSI, Fibre Channel (FC) and FC over Ethernet (FCoE) based block storage area networks (SAN) and file based (NFS and Windows SMB/CIFS) network attached storage (NAS) using IP and Ethernet networks. This has been particularly true by most of the independent storage vendors who have become focused on networked storage (SAN or NAS) solutions.

However some of the server vendors have also jumped into the deep end of the storage pool with their enthusiasm for networked storage, even though they still sell a lot of DAS including internal dedicated, along with external dedicated and shared storage.

The trend for DAS storage has evolved with the interfaces and storage mediums including from parallel SCSI and IDE to SATA and more recently 3Gbs and 6Gbs SAS (with 12Gbs in first lab trials). Similarly the storage mediums include a mix of fast 10K and 15K hard disk drives (HDD) along with high-capacity HDDs and ultra-high performance solid state devices (SSD) moving from 3.5 to 2.5 inch form factors.

While there has been a lot of industry and vendor marketing efforts around networked storage (e.g. SAN and NAS), DAS based storage was over shadowed so it should not be a surprise that those focused on SAN and NAS are surprised to hear DAS is alive and well. Not only is DAS alive and well, it’s also becoming an important scaling and convergence topic for adding extra storage to appliances as well as servers including those for scale out, big data, cloud and high density not to mention high performance and high productivity computing.

Consequently its becoming ok to talk about DAS again. Granted you might get some peer pressure from your trend setting or trend following friends to get back on the networked storage bandwagon. Keep this in mind, take a look at some of the cool trend setting big data and little data (database) appliances, backup, dedupe and archive appliances, cloud and scale out NAS and object storage systems among others and will likely find DAS on the back-end. On a smaller scale, or in high-density rack deployments in large cloud or similar environments you may also find DAS including switched shared SAS.

Does that mean SANs are dead?
No, not IMHO despite what some vendors marketers and their followers will claim which is ironic given how some of them were leading the DAS is dead campaign in favor of iSCSI or FC or NAS a few years ago. However simply comparing DAS to SAN or NAS in a competing way is like comparing apples to oranges, instead, look at how and where they can complement and enable each other. In other words, different tools for various tasks, various storage and interfaces for different needs.

Thus IMHO DAS never left or went anywhere per say, it just was not fashionable or cool to talk about until now as it is cool and trend to discuss it again.

Ok, nuff said for now.

Cheers Gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press, 2011), The Green and Virtual Data Center (CRC Press, 2009), and Resilient Storage Networks (Elsevier, 2004)

twitter @storageio

All Comments, (C) and (TM) belong to their owners/posters, Other content (C) Copyright 2006-2012 StorageIO and UnlimitedIO All Rights Reserved