Storage Facts
Data storage and access is a primary function of a network and selection of the right storage strategy is critical. The following table describes the options for server and network storage.
Method
Description
Direct Attached Storage (DAS)
Direct Attached Storage (DAS) uses storage devices that are connected directly to the server, either internally or contained within an external storage cabinet. Hard disk drives (typically SCSI or possibly SATA disks) are connected to the server through a host bus adapter (HBA).
DAS provides a low-cost, high-performance storage solution.
Data is saved to the storage device using block-level writes. This is faster than writing data as a file.
Storage devices are typically controlled by a single server, so that all access to the storage must go through the server.
If the server fails, access to the storage devices is lost.
Multiple servers can share the storage device, but multiple server access is typically limited to a clustered configuration to provide access to the data when one server is unavailable.
Network Attached Storage (NAS)
With Network Attached Storage (NAS), external storage devices are connected to the network, sharing the network with servers, workstations, and other devices. Client devices access the NAS device to read and write files in the same way that clients access files on a file server.
A NAS device is typically a pared down file server consisting of:
A storage enclosure with terabytes of storage space.
A motherboard (logic board).
One or more network interface cards. Multiple interface cards allow you to perform adapter teaming.
A minimal network operating system.
NAS devices use file transfer, such as Server Message Block (SMB) for Windows clients, to read and write files from the NAS device. File transfer operations are slower than block-level operations.
Storage Area Network (SAN)
A Storage Area Network (SAN) connects multiple servers with multiple external storage devices through a dedicated network. With a SAN:
Storage devices and servers are connected to the private storage area network. Client computers are not connected to the SAN, but communicate with the servers to access files from the storage devices.
All of the devices that connect servers and storage together are called the SAN fabric.
Each server is configured with the storage units on the storage devices that it can access. You can configure multiple servers for each storage unit, or multiple storage units for each server.
Servers are connected to the SAN through an HBA. For redundancy, you can use multiple HBAs to connect the server to the SAN.
On servers, define virtual partitions or virtual disks called Logical Unit Numbers (LUNs). LUNs appear to servers as local disks.
Special networking protocols allow servers to send block-level read and write operations to the storage devices.
Performance is similar to data access from direct attached storage, but with greater distances and shared storage.
When implementing a SAN with Windows Server 2008 or 2008 R2, devices must support the Virtual Disk Specification (VDS).
Partition Style
Description
Master Boot Record (MBR)
MBR is the traditional partitioning method. With MBR, you can have:
Up to 4 partitions
A maximum of 2 TB per partition
With MBR, partitioning information is often stored in hidden locations on the disk or even within the operating system. These locations might vary from vendor to vendor.
GUID Partition Table (GPT)
GPT is a newer partitioning method. With GPT, you can have:
Up to 128 partitions (Windows restriction)
Disks over 2 TB in size
With GPT, partition information is stored on the disk in well-documented locations. Each partition is identified by a GUID number. GPT also provides redundancy for the partition table.
You define storage areas on a disk by creating volumes. The way that volumes are handled depends on the disk type, either basic or dynamic.