Backing Up Data with Unicenter TNG
ARCserveIT, the storage management segment of Unicenter TNG's Enterprise Management component, provides the software necessary to produce backups, restore data, and manage media. Backups can be tricky, but ARCserveIT makes backing up your data easier by automating commonly used backup and rotation methods.
Backup rules of the road
Backing up in your car without looking is certainly dangerous. Similarly, backing up your data without certain guidelines can make a bad situation even worse.
General rules for ensuring that backups do what they're supposed to do:
- Maintain current backups: How much data are you willing to lose? Well, let's rephrase this. In real life: How much data are you able to lose and still recover sufficiently? Most organizations generate enough changes in a day that daily backups are desirable.
- Use a proven backup scheme: Consider the rotation schemes that ARCserveIT has already mapped out and pick one (or build your custom design around a proven schema).
- Back up critical data daily: Especially back up the Common Object Repository (CORe) and other mission-critical databases.
- Know how to restore your data: When recovering from a disaster, make sure you are rebuilding your files or entire system from the correct installation disks and backup media.
- Use off-site storage: Maintain a full set of backups at a protected (from people, fire, water, heat, and so on), off-site location. And don't forget to store at least one set of operating system installation tapes. Tapes should be rotated regularly to ensure current backups are available for disaster recovery purposes.
- Document recovery procedures: Your disaster recovery plan should document everything and be stored off-site. Documentation should include in-house policies, how to recreate your entire system, how to get in touch with key staff members, and operating system documentation provided by relevant vendors (such as Microsoft, IBM, and Novell, among others).
The backup method determines which files in a specific drive or directory are backed up. You identify a backup method when configuring a backup job. When determining which file to back up, several of the backup methods check to see if a file's archive bit is turned on or off. Each file has a special bit (the archive bit) that determines the action ARCserveIT takes when performing backups. An "on" state indicates that the file has changed since the last backup and needs backing up. An "off" state indicates the file has not been changed, and so the file can be skipped in the backup process. An "in-between" state means you could be on or off, and we're no longer talking archive bits.
Full backup methods back up all files, regardless of how the archive bit is set. However, the archive bit can be reset (turned off) depending on the backup method used.
As a general rule, running differential or incremental backup jobs each day and a full backup once a week is a good approach to protecting your data. The differential and incremental backups require less time to perform and, combined with the last full backup, ensure that current data is always backed up and can be retrieved as needed.
Successive differential backups take longer to perform than incremental backups because the differential method backs up anything that has changed since the last full backup. With differential backups, the amount of data being backed up increases each day until the full backup occurs. Therefore, while incremental backups run faster, the differential has fewer media that need to be accessed if it becomes necessary to restore the entire system.
A rotation scheme is a schedule to rotate storage media. When scheduling routine backup jobs, a rotation scheme helps manage media placement; ensures that an adequate quantity of backup materials is used; and that storage and retrieval is handled efficiently. Plan to cycle through multiple sets of storage media for each type of backup job (such as daily, weekly, or monthly) when performing routine backups.
Generally, rotating media according to a schedule adds insurance for data reliability and integrity. For example, using more than one set of tapes to perform daily backups ensures that you can retrieve data from any day of the week prior to a full backup. It also forestalls the possibility that a corrupt backup would thwart recovery efforts.
ARCserveIT enables the following rotation schemes:
- GFS (Grandfather-Father-Son) rotation scheme: The patriarchal naming convention refers to the generations of tapes used for monthly, weekly, and daily backups, respectively.
- User-defined rotation scheme: You can create your own rotation schedule, modifying the GFS schema or working from scratch.
Using media pools
A media pool is a set of backup media that is set aside for a specific job (such as daily, weekly, or monthly backups) and is managed as a unit. With ARCserveIT, a media pool is the set of tapes used exclusively for a particular recurring backup job.
With media pools, ARCserveIT automatically divides each pool into a scratch set and a save set (scratch 'n' save). Any media in a save set can't be overwritten until certain criteria are met — until a certain time period has passed and a certain number of similar but more recent backups have been saved, for example. This prevents the possibility of overwriting Monday's tape on Tuesday (or any tape before its time, as defined by the GFS rotation scheme described below.
A save set tape becomes eligible for reuse once it is succeeded by a minimum number of save set tapes. For example, Monday, Tuesday, Wednesday, and Thursday each have their own set of backup media (the save set) that is retained for six days (the retention period). On the seventh day, the save set becomes the scratch set, so it can be reused (overwritten). In other words, it's Monday, and the daily media pool from last Monday's backups becomes part of the scratch set to be used for this Monday's (today's) backups. Once today's backups are completed, the scratch set for today becomes the Monday save set that is retained all week.
GFS a break
The GFS rotation scheme uses three media pools for backups: Daily, Weekly, and Monthly. Each pool has a default retention period (length of time the storage media needs to be retained before you can overwrite it) and number of storage media to save (for example, however many tapes are required to perform a daily or weekly backup).
- Daily pool (the Son generation): The storage media (generally, tapes) used for daily backups. By default, tapes are retained six days and reused after four daily backups. If dailies are run Monday through Thursday, the following Monday would recycle media from the previous Monday. Typically Friday is not part of the daily pool; rather, Friday's run comprises the weekly backup and uses media from the Weekly pool.
- Weekly pool (the Father generation): The storage media used for weekly backups. By default, tapes are reused after five weekly backups.
- Monthly pool (the Granddaddy): The storage media used for monthly backups. By default these tapes are retained for 12 months before being reused.