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. Networkedattached storage NAS An NAS unit is essentially a selfcontained computer connected to a network with the sole purpose of supplying filebased 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 generalpurpose 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 browserbased 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. Directattached 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 filebased 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 highspeed 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 highspeed blocklevel 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. Allinone networked storage An allinone network storage device combines the capabilities of SAN and NAS providing flexibility to businesses.

By combining block and filelevel storage clients on the LAN have direct access to shared files on the allinone 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.

Stephen J. Richards has 25 years experience in Data Management and Information Technology. This information is provided as a public service by Neon Enterprise Software a leading provider of IMS outsourcing. For more information please visit http://www.neonesoft.com.



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