Netbackup Important Terminologies -- Part 1

Master Server

• Acts Enterprise Media Manager server (contains info about robots, drives , Storage Units etc.,).
• Control unit or Centralized management server of Netbackup architecture.
• Controls all the backup scheduling for each media server.
• Each of the media server performs the actual backup operations under direction from the master and backup data stays local to the media severs or to their corresponding storage units (like Tape) .
• Also tracks the media being used.
• Stores the catalog information (what are the backups taken) information.
• Master server should be the dedicated server, in some cases both master and media server resides in same server.

Media Server or why media server is required ?

• Assistance for master server. 
• Data mover in the netbackup architecture.
• To increase performance by providing additional processing ability and better distribution of workload (load balancing).
• Master server communicates client through Media, all the clients are connected to the media server only.
• Media is divided into 2 , disk storage and tape. Backup has been written to tape through media server instead of writing directly to the Tape. It is due to whenever we need to restore recent backup it take much time to restore it from tape instead directly from the server.
• All the tape libraries should be connected to Media server only.               

Backup Client

• During the backup or archive the client system generates the backup as a data stream and sends it across the network to the media server (tape).
• No license required for client servers. 

Archive bit

• The archive bit is a binary bit. As such, it is either 1 or 0.
• Set 1 and clear or reset 0. It represents whether the file has (1) or has (0), since the last full backup.

Difference between backup and archive

     When a backup is made, a copy of the file is written to media. When an archive is made, a copy of the file is written to the media and then original file is deleted.

Difference between backup and “True image”
    A regular backup can backup and restore individual files. 
    A TI backup is a snapshot of files done at the directory level at a certain point in time. Additionally, when a “True Image” backup is restored, the directory restored will be brought to the same state as when it was backed up.
   Any files or sub-directories that did not exist at the time of backup will be deleted when the restore occurs if it is restored to the same location. 

Types of Backup in Netbackup
a)Full Backup
     Is the starting point of all the backups, contains all the data in the folders and files that are selected to be backed up.
Advantages: Restore is fast
Disadvantages: Backup is slow and Consume more space.
b)Differential Incremental (VPS)
     Takes the backup of the changes since the latest backup.  Archive bit is reset. Backup had taken based on the timestamp.
Advantages:
      Less space occupancy in the tape, since only the changes had been taken as backup.
      Backup window is shorter
Disadvantages:  
      Slow restore, (Backup window is longer) since the images are stored in scattered manner, while restoring, organizing the data will take time and restore.
      In case of retention, to restore all files requires last full backup and all the differential backups since last full backup, so all the differentials must be kept until the next full backup occurs.
c) Cumulative Incremental
       A cumulative incremental backup is the backup of all files that have changed since the last full backup
Advantages:
     Fast restore, since the last cumulative incremental is required for a complete restore ( in addition to full)
Disadvantages:
     More space occupancy in Tape/media
     Backup window is longer
d) Synthetic Backup
    A Synthetic full or cumulative incremental backup is a backup assembled from previous backups.
    Can be written to tape or disk storage units, or a combination of both. 
e) User initiated Backup
     Its also called manual backup, initiated by the user.
f) Archive Backup
     After taking the backup the original file is deleted.

Difference between Differential and Cumulative incremental

Differential Incremental Backup

    
If the disk fails after sometimes on Jan 4 (after backup) the full backup and 3 diff incremental backups requires to restore data 

Cumulative Incremental  Backup

 

   If the disk fails on Jan4, only Jan4th cumulative incremental backup is required to restore the data. 

Define Catalog Backup   

• Netbackup have special kind  of backup called “Catalog Backup”. 
• It is an internal database that contains backup information of the files that have been backed up and media where it stored and NB configuration.
• The catalogs also contain the information about the media and storage devices.
• Netbackup requires the catalog information in order to “restore backups” , so it is extremely important to configure a  catalog backup before using  netbackup for regular client backups.
• Also used to search for a backup image in order to verify the contents of media with what is recorded in the NB catalog. To duplicate a backup image, to promote a backup image from a copy to the primary copy. To import expired backup images or images from another NB server.
• Hence loosing the catalog means loosing the backups. 
• In  General Catalog Backup is configured as “FULL backup”.

Parts of Catalog 
      There are 3 parts of catalog 
         image database
         NB relational database
         NB configuration files
i)Image database 
      Biggest part of the catalog image database.
   root@MasterServer # cd /usr/openv/netbackup/db/images/
   root@MasterServer # ls      
   Appserver Webserver dbserver 
      This images folder contains subfolders for each server and its corresponding image.
   root@MasterServer #cd Appserver/
   root@MasterServer #ls -lrth
  drwxr-xr-x   4 root     other          7 Apr 29 06:34 1332000000
  drwxr-xr-x   4 root     other          7 Jun  2 06:36 1335000000
  drwxr-xr-x   4 root     root          49 Jul  1 18:41 1340000000
  root@MasterServer # cd 1332000000
  root@MasterServer # ls -lrth
  total 30
  -rw-------   1 root     other         35 Mar 27 06:32     Appserver_Policy_1332665618_FULL.f.Z
-rw-r--r--   1 root     other       1.3K Mar 27 06:32   Appserver_Policy_1332665618_FULL
  drwxr-xr-x   3 root     other          4 Mar 29 01:04 tmp
  drwx------   2 root     other         11 Apr 18 06:33 catstore
ii) Relational DB files
root@MasterServer # cd /usr/openv/db/data/
root@MasterServer # ls
DARS_DATA.db        DBM_DATA.db         EMM_DATA.db         NBAZDB.db           NBAZDB.log          NBDB.log  DARS_INDEX.db       

iii) NB Configuration Files
   The configuration files include flat files concerning policy, schedule information, licensing information etc ., in the folder /usr/openv/var

How to recover the catalog in case of accidental removal or Master server got crashed?
      There are 2 way of procedures for catalog recovery 
          i) Actually, the catalogs are stored in "Stroage LUN" hence if the master server got crashed, then we need the NB master server in some other server and map the LUN to the server  and process catalog restore activity.
        ii) If primary (tape) catalog backup files the secondary backup is converted into Primary if the secondary is in expired state, first we want to unexpire and update.