Enterprise Storage Options

Data, these days, is the fastest growing component on your enterprise network. But where does all the data reside? In storage devices. Various techniques have been used from time to time to store data efficiently, and to provide fast and smooth access. In this article we’ll look at some of the storage options available for an enterprise.

Hard-disk drives

The most common storage device, the hard-disk drive can now store anywhere up to 100 GB of data. And with the prices of hard disks coming down, you can easily get a fast, high-capacity drive at a decent price. For example, the Maxtor 100 GB drive we reviewed in our October 2001 issue costs around

Rs 12,800.

There are various factors that affect the performance of the drive, such as the seek time, spindle speed, data transfer rates, CPU utilization and latency. Disk drives are also available in two different interfaces: IDE (Integrated Device Electronics) and SCSI (Small Computer System Interface). An interface is basically the channel over which data flows to and from the hard disk. IDE is the most popular and commonly-used interface in disk drives today. The current standard in IDE is UltraATA/100, which allows burst data transfer rates of up to 100 MBps. SCSI drives, on the other hand, are much faster than IDE drives, but also more expensive. An 18 GB Ultra 160 SCSI drive, for example, would cost you around Rs 16,720.

They are commonly-used in high-end appliances, such as servers.

Backup options

CD-Rs/CD-RWs, tape drives, removable storage devices

One of the cheapest options to back up data is CD-Rs and CD-RWs. A branded CD-R and CD-RW media disk, for example, would cost around Rs 40 and Rs 200 respectively. A CD-ReWriter can cost you anywhere between Rs 8,000-14,000. The Aopen CD-ReWriter, for example, we reviewed last month costs Rs 8,000.

Another backup option for mobile professionals is portable, removable storage devices. A range of devices are available in this segment ranging from Zip/Jazz drives, pen drives, mobile disk drives, to flash cards. These devices are available in different capacities for different prices, so if you are a frequent traveler you can choose one that meets your requirement and suits your pocket too. (See box below for some such products and their prices.)

• Iomega 100 MB USB Zip Drive: Rs 5,700
• Iomega 100 MB Parallel Zip Drive: Rs 6,550
• Iomega 2 GB Jaz Drive: Rs 24,250
• The WeP 32 MB Pen Drive: Rs 5,500
• TrekStore USB 20 GB mobile drive: Rs 19,900

The other options to backup your servers and workstations are DLT/DAT tape drives. DLT (Digital Linear Tapes) and DAT (Digital Audio Tapes) differ in the type of recording technologies they use. These drives can back up large chunks of data and are also quite expensive. For example, HP’s SureStore DLT1e drive can back up 80 GB of data and costs Rs 80,000. 



FireWire drives

Developed by Apple, the FireWire drives are used for high-speed data communication and for large bandwidth applications, such as online video-editing and video conferencing.

The benefit of using such drives is its high data-transfer rates and plug and play functionality. These drives are capable of data transfer speeds up to 1.6 Gbps. Most of the Apple products ship with a FireWire port these days. Some of the latest drives, such as Iomega’s Peerless drives, also ship with a FireWire interface.

Direct Attached Storage

DAS (Direct Attached Storage) comprises storage devices such as hard disks or tape drives connected directly to a network server. It could be inside the same box as the server, or reside outside and be connected through a cable.

This is the most basic method of storage, and the most widely used, as it’s simple, and doesn’t require too much time to setup.

A DAS setup can have a single hard disk, multiple independent hard disks called JBOD (Just a Bunch of Disks), or an array of hard disks configured for fault tolerance, known as RAID (Redundant Array of Independent Disks). The most common types of media and protocols used in DAS are SCSI, fiber channel, and SSA (Serial Storage Architecture).

DAS is easy to implement, and gives reasonably good performance. It also has relatively lower acquisition and administrative costs. However, it has its limitations. Its capabilities are limited to the server it’s connected to. So if the server is down, users can’t access their data. It can’t be connected over long distances, and the storage capacity is also limited compared to NAS and SAN. DAS devices also pose management problems, as you have to manage the data on a server-by-server basis.

Network Attached Storage

An attempt to overcome problems associated with DAS led to the development of NAS (Network Attached Storage). Unlike DAS devices, which connect to a particular server, NAS devices connect directly to your existing Ethernet network and are independent of the server. So, if the server fails due to some reason, data is still available to users on the network.



NAS devices can be placed anywhere on your network and can be accessed by any user. Its function is similar to that of a network printer, which can be accessed by anyone when required. NAS devices support most network protocols such as NFS for UNIX, CIFS for Microsoft, FTP, and HTTP. This makes them useful for heterogeneous networking environments.


NAS devices consists of a number of hard-disk drives and come with their own OS and management software. They can be used for a variety of applications including Web caching for proxy servers, backup, databases, print spoolers, or simply as file servers. Storage capacities for NAS devices can range from 2 GB to over 2 TB.

Another benefit of NAS is that it allows organizations to setup a storage solution using their existing Ethernet backbone, without investing in a separate network. On the flip side, since NAS operates on networks that were primarily designed for data transmissions and not storage, performance issues such as network congestion arise. Also, if you exceed

your storage capacity than you must add another NAS device.

Storage Area Networks

The latest technology in the area of storage is SAN (Storage Area Networks). As the name suggests, a SAN is a separate network linked to your company’s main network via a high-speed interface like a fiber channel or SCSI. This sort of a solution is useful for companies having high transaction volumes like banks and customer-service oriented organizations that need quick access to data at any point of time.

A SAN network consists of multiple storage systems and servers and is much faster than a NAS system. That’s because unlike NAS, the various storage devices in a SAN are connected through a high-speed interface, such as fiber channel or SCSI. Fiber channel typically has a data transfer rate of 1 GB/sec. SCSI transfer rates are lower than fiber-channel, about 80 MB/sec. However, in future these devices are likely to communicate over Gigabit Ethernet using iSCSI or Fiber channel over TCP/IP

(FCIP).

The various storage devices in a SAN interface with the company’s main network via switches and hubs, and can be simultaneously accessed by multiple servers and computers. All SAN components are controlled using SAN management software, which allows users and system administrators to remotely control its functioning.

SAN architectures

Fiber-channel SANs can be deployed in two topologies: Arbitrated loop and Fabric, also called switched fabric. The arbitrated-loop topology can be compared to the token ring topology and enables you to connect up to 127 fiber-channel enabled devices. However, instead of sending a token, devices in this topology send a signal that tells other devices that they want to gain control of the transmission medium. When one device gains control, other devices have to wait until that device’s I/O cycle is complete. The main disadvantage of this topology is that servers-connected in this topology have to share the available bandwidth.

On the other hand, in switched-fabric topology, servers share the bandwidth only when others servers need to access the same storage device. However, if each server needs to use a separate device, then it can make use of the entire bandwidth. This topology provides a virtual dedicated connection between the network servers and the SAN, and lets you inter-connect up to 64,000 devices. The switched-fabric topology offers better SAN performance than the arbitrated-loop topology. 



Different SAN solutions are available from different vendors. Some offer complete SAN solutions with all necessary products, such as hubs and switches. Others, however, provide SANs that include only the hard-disk drive enclosure with the specialized OS. You need to add other SAN components such as bridges, hubs, and switches later.

Neelima Vaid