Tuesday, March 2, 2010


Different Types Of Data Storage | Advantages And Disadvantages Of Online Nearline And Offline Storage And Backup

What are commonly referred to as types of backups should really be called levels of backups. What level of backup you want dictates how many files make it to tape (or your backup media of choice). This post describe the three main types of backups: full backup, incremental backup, and differential backup.  Read more

File storage can be conveniently divvied up into the following categories:
  • Online
  • Nearline
  • Offline
Online: Online usually means “connected.” In the storage arena, online means files that are immediately available. If you try to access them, they are there (depending on the speed of your connections). 

In the actual world of computing, the files stored in your computer’s hard drive are “online” storage in relation to you. Even if the files are on a server in Australia and you are in Omaha, Nebraska, the files are still “online” as long as you have some kind of network connection to them. The files are immediately accessible.

Online Backups: An “online backup” refers to a backup that is done when everything is online—the server performing the backups and the computers that are being backed up. With an online backup, you don’t make a computer unavailable to back up its files. You keep it functioning on the network, allowing its users to continually access its data.

Figure : Online backup

The advantage of online backup is that all the data is available all the time. From the user’s perspective, it makes no difference whether the file is currently being backed up or not. The user will be able to access it.

The disadvantage of online backup is that it uses up precious network bandwidth. If not designed properly, an online backup could result in slower performance in the general network, as well as on the computers directly affected by the backup process.

Nearline: As the word itself implies, “nearline” refers to files that are stored nearby. They are not immediately accessible, but they almost are. It takes a little effort to obtain the files, but you don’t have to wait for long.

When a system uses nearline storage, infrequently used data is moved out of the main network into a secondary system. The secondary system is referred to as nearline.

Nearline Backups: In a “nearline backup,” the secondary system archives the data in tapes or other media. This occurs after a certain time configured by the administrator.
Figure2: Nearline backup

While the data is on the nearline system, it is still readily available. When a user requests data that is still on the nearline system, the system can put the data back into the main network without any apparent delay to the user.

The advantage of nearline backup is that it allows the most frequently used data to be constantly accessible to users without taxing the network bandwidth or computer resources.

The disadvantage of nearline backup is that sometimes users will request data that has already been archived, and they will have to wait for the data to be restored before being able to access it.

Offline: Of course, you wouldn’t keep all your files in one place.  Why, you’d lose everything! That’s why many people store their data “offline.”

The files are stored in a location that is not immediately accessible. The offline files may be stored in a different server and even in a different location. In your company, data may also be stored in another location.

Offline means that the data is totally disconnected from the network. This is the data that would require the most time to recover, since physical measures may be necessary to get the data to the restore location. However, it is the safest data. Since it is totally disconnected from the network, it cannot be corrupted or accessed by hackers.

Offline storage allows you to store the data at locations separate from those that house the main servers. Tapes may even be stored by an offline data storage company, which safeguards tapes in its own secure warehouses. If physical disaster strikes the main office, the data is still safe if the tapes have been stored at other sites.

Offline Backups: Offline backups involve making a computer unavailable when its data is being backed up. The user would have to wait until the backup is finished before having access to the data again.
Figure3: Offline backup

The advantage of offline backups is that little to no network bandwidth is used; therefore, there will be no slowdown in network performance when a backup is being made. In environments where the data is only accessed during business hours, it is easy to schedule a backup to be performed during off hours. That way, for all practical purposes, the data will be continually available during the time when it is needed.

The disadvantage of offline backups is that the data becomes unavailable for a certain time, and this may be unacceptable for web sites and other systems that need to be up 24 hours a day.


About bench3 -

Haja Peer Mohamed H, Software Engineer by profession, Author, Founder and CEO of "bench3" you can connect with me on Twitter , Facebook and also onGoogle+

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