Monday, January 21, 2013

What is a backup

What is a backup: Backup is copying data from one place to another in case the original is corrupted   
                                  or deleted.   

Ø  Backups are the secondary copy of primary data. The purpose of backups is to recover primary data if it’s damaged, deleted, or corrupted. Therefore, a backup is a secondary copy of primary data.
Ø  Backups recover data that was damaged, deleted, or corrupted. This is the only purpose for backups. If a file is deleted or damaged, you can restore it from backup copies.

What Needs to Be Backed Up: Companies need to back up three types of data:
Intellectual property: This is the information about a company’s core competency.
Customer data: Examples range from scanned copies of patient x-rays to market research information and records about the buying patterns of particular market segments.
Operational data: This last category includes every other kind of data in the organization. It can include data about where organizations purchase supplies to build products to information.

Backup Tool
 Many backup tools are available in market Linux has several tools for backing up and restore which are given below.
dump / restore : Old tools that work with filesystems, rather than files.

Rsync:  is a program that behaves in much the same way that rcp does, but has many more options and uses the rsync remote-update protocol to greatly speed up file transfers when the destination file already exists.

tar: A standard backup tool,

cpio : It is hard to use because of the unusual way in which the command must be entered.

dd : The dd command is one of the original Unix utilities and should be in everyone's tool box

Mondo : is reliable. It backs up your GNU/Linux server or workstation to tape, CD-R, CD-RW, DVD-R[W], DVD+R[W], NFS or hard disk partition

Dar: dar is a shell command that backs up directory trees and files.

Many other commercial or free software back up tools are also available, like EMC Networker, EMC Avamar, HP Data Protector, Symantec Netbackup, etc.
Types of Backup
 There are different kinds of backups

Full Backup: Full backup is a backup of the complete data on the production volumes at a certain point in time. A full backup copy is created by copying the data on the production volumes to a secondary storage device

Advantages:                       Restore is the fastest
Disadvantages:                                 Backing up is the slowest
The storage space requirements are the highest


Incremental Backup:  Incremental backup copies the data that has changed since the last full or incremental backup, which-ever has occurred more recently.

Advantages:                       Backing up is the fastest
                                The storage space requirements are the lowest

Disadvantages:                 Restore is the slowest

Differential Backup: Cumulative (or differential) backup copies the data that has changed since the last full backup. This method takes longer than incremental backup but is faster to restore.

Advantages:                       Restore is faster than restoring from incremental backup
Backing up is faster than a full backup
The storage space requirements are lower than for full backup

Disadvantages:                 Restore is slower than restoring from full backup
Backing up is slower than incremental backup
The storage space requirements are higher than for incremental backup


Synthetic(or constructed) :- full backup is another type of backup that is used in implementations where the production volume resources cannot be exclusively reserved for a backup process for extended periods to perform a full backup. It is usually created from the most recent full backup and all the incremental backups performed after that full backup. A synthetic full backup enables a full backup copy to be created offline without disrupting the I/O operation on the production volume.

Network Backup: Network backup usually means backing up a client to a backup server, this means the client sends the files to the server and the server writes them to backup medium.

Dump Backup: Dump backups are not ordinary file by file backups. The whole disk partition or file system is "dumped" to the backup medium as is. This means it is also necessary to restore the whole partition or file system at one go. The dump backup may be a disk image, which means it must be restored to a similar disk with same disk geometry and bad blocks in same places.



Level 0 -- 9 Backup: Level 0 to 9 backups are a finer grained version of incremental backups. Level N backup means backing up everything that has changed since a same or lower lever backup. Check the backup can be restored, with original file owners, permissions and timestamps. To be useful, you must be able to restore the backup. Very often not only the contents of file are important, but their time stamps, permissions and owners. Check that you can restore the backup so that all these are preserved.

Backup Methods: - There are two types of methods to deployed for backup Hot backup and cold backup are the two. They are based on the state of the application.
Hot backup: when the backup is performed. In a hot backup, the application is up and running, with users accessing their data during the backup process.
Cold backup: the application is not active during the backup process.

Saturday, January 19, 2013

Data Storage in Short



Data Storage
 The term data storage can refer to anything with information recorded on it. Using this broad definition, a hardback volume of an encyclopedia, an audio cassette of a pop song, and even a piece of paper with random words written on it would all be considered examples of data storage. The most popular definition of the term limits it to only the storage of information on computers and similar devices.

Data storage in terms of computer Everything a computer “knows” or is able to “know” is called computer data. This includes e-mails, text files, digital pictures, and databases.  Computer data storage is the holding of data in an electromagnetic form for access by a computer processor which can be divided into two main categories: primary data storage and secondary data storage.

Primary data storage: What a computer “knows” at any given time is technically what information a computer’s central processing unit (CPU) can directly access. This information is called memory, and the components that store it are considered primary data storage. Memory is mainly stored on Random Access Memory (RAM). There are many types of RAM, but they usually come in the form of modules that plug into a specific slot inside the computer. Primary data storage is constantly being erased and rewritten, most often from secondary data storage.

Secondary data storage represents all of the other types of computer data storage not included in primary data storage. Internal hard disk drives, CD-ROM disks, and flash memory sticks are all examples of secondary data storage. Because there are so many different types of secondary data storage, this category can be further divided into three different areas: on-site, removable, and off-site data storage.

 Ø On-site data storage represents any type of storage device that is designed       to remain with the computer or at a single location where the computer is housed. The most common on-site data storage device is a hard disk drive, and it is included in almost every personal computer. Solid state drives and network attached storage are also examples of on-site storage devices.

 Ø Removable data storage is any type of data storage that is designed to be easily removed from a computer. Removable data storage has become more common than on-site data storage in modern times. The big disadvantage of removable data storage used to be that data access time was much slower than on-site data storage, but speed improvements have decreased this penalty to within acceptable limits for many common applications. CD-ROMs, DVD-ROMs, USB flash drives, and portable hard disk drives are all examples of removable data storage. Off-site data storage is one of the most recent types of data storage.

 Ø Off-site data storage is stored away from the computer at a distant location. This data can then be accessed either by a direct call or through the internet. Off-site data storage has the advantage of being available if something happens to the on-site computer system.
                         

Storage Architecture’s:  In recent years, enterprise data storage has seen explosive growth in demand in the following areas

Ø  Capacity – the amount of data storage space is increasing. 
Ø  Performance – the bandwidth for delivering storage content is growing to match the increased speed of computer processing power, the speed of data communication networks, and the speed requirement of emerging applications such as multimedia applications.
Ø  Availability – as people and enterprises become more and more reliant on the content in the data storage
Ø  Scalability – the data storage solution must not only be able to satisfy the current storage requirements, but also be easy to grow to address the increased demand of future applications.
Ø  Cost – the cost of ownership needs to be reduced. 

Storage ModelsI will discus later about below three storage models:

>>>Direct Attached Storage (DAS)
>>>Storage Area Networks (SAN)
>>>Network Attached Storage (NAS)







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