Centralizing Data Storage

By: Stephen J. Richards

Management of business data is becoming ever more complex and important with increasing pressures of security, regulatory compliance, and corporate governance. Technology is allowing businesses to create and store exponentially more data.
Understanding how to make the most of your data storage and
centralizing it when possible can help staff in spending less time handling repeated storage and worrying about backup failures. Below are the four types of data storage.

1. Networked-attached storage - NAS - An NAS unit is essentially a self-contained computer connected to a network, with the sole purpose of supplying file-based data storage services to other devices on the network. The operating system and other software
on the NAS unit provide the functionality of data storage, file systems, and access to files, and the management of these functionalities. The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it.

NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser program to their network address. NAS systems contain one or more hard disks, often arranged into logical, redundant storage containers or RAID arrays (redundant arrays of inexpensive/independent disks).

NAS removes the responsibility of file serving from other servers on the network. A NAS appliance is a simplified form of file server. Authorized clients can see folders and files. Installation consists of rack mounting, connecting power and Ethernet, and configuring via a simple browser-based tool. NAS devices are frequently used to consolidate file services. To prevent the proliferation of file servers, a single NAS appliance can replace many regular file servers, simplifying management and reducing cost and workload for the systems administrator.

2. Direct-attached storage - This is the most common form of server storage. The disks may be internal to the server or they may be in an array that is connected directly to the server. Either way, the storage can be accessed only through that server.

The main protocols used in DAS are SCSI, SAS, and Fibre Channel. Traditionally, a DAS system enables storage capacity extension for a server, while keeping high data bandwidth and access rate. A typical DAS system is made of one or more enclosures holding storage devices such as hard disk drives, and one or more controllers. The interface with the server or the workstation is made through a HBA (Host Bus Adapter).

Backups must be either performed on each individual server with a dedicated tape drive or across the LAN to a shared tape device, consuming a significant amount of bandwidth. Storage can only be added by taking down the application server, adding physical disks, and rebuilding the storage array. In small institutions this setup can work well, but it gets very difficult to manage as the number of servers increases. Backups become more challenging, and because storage is not shares anywhere, storage utilization is typically very low in some servers and overflowing in others.

3. Storage Area Networks - SAN - storage area network (SAN) is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries and optical jukeboxes) to servers in such a way that, to the operating system, the devices appear as locally attached.

Although cost and complexity are dropping, as of 2007, SANs are
still uncommon outside larger enterprises. By contrast to a SAN, Network Attached Storage (NAS) uses file-based protocols such as NFS or SMB/CIFS where it is clear that the storage is remote, and computers request a portion of an abstract file rather than a disk block.

Historically, data centers first created "islands: of SCSI disk arrays. Each island was dedicated to a application, and visible as a number of "virtual hard drives" (i.e. LUNs). Essentially, a SAN connects storage islands together using a high-speed network, thus allowing all applications to access all disks.

Operating systems still view a SAN as a collection of LUNs and usually maintain their own file systems on them. These local file systems, which cannot be shared among multiple operating systems/hosts, are the most reliable and most widely used. If two independent local file systems resided on a shared LUN, they would be unaware of this fact, would have no means of cache synchronization, and eventually would corrupt each other. Thus, sharing data between computers through a SAN requires advanced solutions, such as SAN file systems or clustered computing.

Despite such issues, SANs help to increase storage capacity utilization, since multiple servers share the storage space on the disk arrays. The common application of a SAN is for the use of transactionally accessed data that require high-speed block-level access to the hard drives such as email servers, databases, and high usage file servers. In contrast, NAS allows many computers to access the same file system over the network and synchronizes their accesses. Lately, the introduction of NAS heads allowed easy conversion of SAN storage to NAS.

4. All-in-one networked storage - An all-in-one network storage device combines the capabilities of SAN and NAS providing flexibility to businesses.

By combining block and file-level storage, clients on the LAN have direct access to shared files on the all-in-one device, and application servers share storage. Instead of having to predict how much storage will be required for file sharing versus application data, storage can be allocated from a central pool.

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