DAS: Ideal for Local File SharingDirect-attached storage, or DAS, is your hard drive or storage devices inside your host server or directly connected to a single server such as RAID arrays or tape libraries. In order to connect to the storage device, you must access the host server. This is in contrast to a SAN or networked storage. SAN appliances are connected to servers over a network and not directly. DAS comprises a large majority in today's IT infrastructures but many SMBs are finally realizing the necessity to transition away from DAS to networked storage.
SANs: Ideal for High Availability for Block-Level Storage and for Server VirtualizationWhile DAS is ideal for local file sharing for small companies where workgroups need to share information over, it is not a good choice for storing VMs in a server virtualization environment. Most customers who continued using DAS, did so because it had the reputation of being simple and inexpensive. Today, SMBs can find SAN options that are also simple and inexpensive yet are much better for data protection and management than DAS approach. Additionally, SAN is the only way to increase application and data availability for server virtualization.
In contrast to DAS, which is optimized for file sharing at the file level, SANs are able to quickly move large blocks of data on the network. Given this ability, SANs are the best way to ensure predictable performance and significantly increase the availability and reliability of applications and data, especially for VMware, Hyper-V and XenServer environments. Also, unlike direct-attached storage, excess capacity in SANs can be pooled which results in a very high utilization of storage resources.