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Network Storage Backup & Restore

Analysts have considered all the costs and come up with some figures:

$50,000 is the average hourly cost per megabyte to re-create and restore data. $18,000 is the average hourly cost of downtime for PC networks. Then there is the cost of downtime. The out-of-pocket expenses associated with downtime hide a wealth of other costs, including loss of customers and impact on an enterprise's reputation and image. The average cost of downtime ranges from approximately $90,000 per hour of in the transportation industry (airline reservations) to $6.5 million for large brokerage houses in the finance industry (as reported by Contingency Planning Research).

Clearly, data protection is business protection. Especially today, when business has become so dependent upon information.

The Solution

Take the time to develop effective backup, archive, and disaster recovery programs. Sun can help you do that--with high-quality backup products and customized Professional Services. This article focuses on backup.

"People don't plan to fail; they simply fail to plan."

Backup: Your First Layer of Protection

Backup is simply making a copy of files from a hard disk onto tape or some other medium so that you have a redundant copy in case there is a problem with the original. Backup also provides version histories, giving you the ability to review the evolution of a document or revert to previous versions when necessary.

An effective backup process, however, requires more than a single layer of redundancy on a single type of media. Here are some hints in creating an effective backup process.

1. Create a multi-layered backup schedule.

    It takes many copies of files stored on separate pieces of media--in separate locations--to fully ensure that data is protected. You need to develop a multi-tiered backup system with a well-defined policy for media rotation.

    Most files don't change from one day to the next, so most companies don't need to back up every file every day. Three different backup levels are commonly used:

    Full backup -- usually includes the entire system and all its files.

    Incremental backup -- includes only the files that have changed since the last full backup.

    Differential backup -- includes every file that is new or has changed since the last full backup.

    Within any of these three levels, either individual file or disk image methods can be used for backup (image backups take a snapshot of your entire disk and send it to tape).

2. Rotate the media according to a well-defined schedule.

    Media rotation is an important part of a layered backup schedule. Two media rotation schemes are commonly used to provide a comprehensive backup program: the Grandfather-Father-Son schedule, and the Tower of Hanoi scheme.

    Grandfather-Father-Son: This scheme uses daily (Son), weekly (Father), and monthly (Grandfather) backup media sets. Four backup media set are labeled for the day of the week each backs up; for example, Monday through Thursday. Typically, incremental backups are performed on the Son media, which is reused each week on the day matching its label. The Father media is reused monthly; and the Grandfather media records full backups on the last business day of each month. Each of these media may be a single tape or a full set of tapes, depending on the amount of data you need to back up.

    Tower of Hanoi: This scheme uses more media sets than the grandfather-father-son technique for increased safety. One media set A is used every other backup session; the next media set B starts on the first non-A backup day and repeats every fourth backup session. Media set C starts on the first non-A or non-B backup day and repeats every eighth session. Media set D starts on the first day when there is no other backup session and repeats every 16th session. Media set E alternates with media set D.

    Thus, the most frequently used media sets have the most recent copies of a file, while less frequently used media retain older versions.

3. Don't skimp on media quality.

    Losing data is expensive. Purchasing high-quality backup media is not. We recommend that you invest in high-quality, high-capacity tape for your servers. Choose a product with proven performance and durability as well as high capacity.

    Sun offers Sun-qualified media through eSun for all of Sun's removable media storage products.

4. Handle media with care.

    Your best-laid backup plans won't do much good if the backup media isn't cared for properly. Never wait for the system to reject your media; follow these guidelines to ensure your media won't fail:

    Inspect media for damage BEFORE use Acclimate media before use Store media in specially designed racks and storage boxes Write-inhibit the media before long-term storage or data interchange Conduct periodic clinical cleaning of the storage



Back-Up and Test Your Back-Up's Frequently!

Always Run Scandisk and Defrag in Safe-Mode

Backup Methods and Rotation Schemes
February 21, 2003


Here are the most common backup methods:

  • Full includes files whether they have been changed or not;
  • Differential includes all files changed since the last full backup, whether they have been changed since the last backup operation or not;
  • Incremental includes only those files that have changed since the last backup operation of any kind.


To choose a method, you must first weigh three factors: the capacity of your tape format, the period of time or window available for your backup, and the level of urgency experienced by those on your network when a file restoration is necessary. For example, conducting full backups on a daily basis will require both large amounts of tape and a long period of time. But doing so will facilitate rapid and easy restoration because you will need only one tape to pull data from. On the other hand, weekly full backups combined with daily incremental backups will conserve tape and shorten the daily backup period, though data recovery would require the last full backup and each subsequent incremental backup up to the most current—a process that can seem to take forever when there are needy users waiting for a file.

After you select a backup method, you need to pick the most appropriate rotation scheme for your organization and network needs, which can reduce media costs and extend the longevity of your tapes while ensuring that every file is protected. Here are the two most common ones that provide the best compromise between backup window and number of tapes.

Grandfather-father-son (GFS) is probably the most common rotation scheme. The grandfather backup is essentially a monthly full backup that is stored off-site, the father is a weekly full backup that is kept on-site (eventuallymoved off-site or recycled, depending on your organization's needs), and the son is a daily incremental backup that is kept on-site (possibly moved off-site along with its accompanying father or recycled). It's probably a good idea to preserve grandfather tapes for a full year and fathers and sons for a month before reuse. This type of scheme requires 20 tapes for a single year.

The Tower of Hanoi scheme is a common alternative to GFS that is secure and cost-effective but more complex. This method requires you to perform a full backup on five tapes labeled A, B, C, D, and E. Tape A is used every other backup session, tape B every 4 sessions, tape C every 8 sessions, tape D every 16 sessions, and tape E every 32 sessions, or once a month. This allows for easy file restorations, because you don't have to shuffle through partial backups, and it is more cost-effective than GFS because it uses fewer tapes. The Tower of Hanoi method's chief disadvantages are the need for a large enough backup window to accommodate daily full backups and its complexity, which means you should make sure your backup software can automate tape


Backup Methods:

(Courtesy PC Magazine)

Tower Of Hanoi

Tower of Hanoi is based on a mathematical puzzle. A series of rings or disks are stacked in size order, the largest on the bottom, on one of three poles. The object is to move all of the rings to the third pole. But you can move only one ring at a time, and you can't place a larger ring on top of a smaller ring. The secret is to shift the first ring every other move (moves 1, 3, 5, 7, 9, 11...), the second ring at intervals of four moves (moves 2, 6, 10...), the third ring at intervals of eight moves (moves 4, 12...), and so on.

The Tower of Hanoi rotation scheme lets you keep several current copies of data, several week-old copies, and a few month- or year-old copies.

Each tape set is used a different number of times. When a new tape set is added, it is slated to be reused every other rotation. Older tape sets are used every fourth rotation, every eighth rotation, and so on. You can perform a tape-set rotation daily or weekly. For example, if you have five weekly tape sets labeled A, B, C, D, and E, your tape rotation would look like this: A B A C A B A D A B A C A B A E (each letter represents a week of backups).


Round Robin

Round Robin uses a single tape set for each day of the workweek. This ensures that you will never lose more than a day's worth of data, but it keeps only a week's worth of your information.


Grandfather, Father, Son (GFS)



GFS is the most common tape rotation method. The number of tape sets you use is based on the number of workdays that you add data to your network. It works as follows:

Back up data on a different tape set every working day. If your backup cycle is based on a five-day workweek, you will need four daily tape sets (a fifth tape set comes into play later). You can perform full, incremental, or selective backups during the week.

On the fifth day, you will use a weekly tape set. You will need three weekly tape sets.

In the fourth week, you will need a monthly tape set. Since there are 13 four-week cycles in a year, you will need 13 "monthly" tape sets.

The GFS method is easy to use if you remember to label your tapes. Also, since the daily tapes are used more frequently than the weekly and monthly tapes, you will need to replace them more often.



Six-Cartridge Weekly Backup Principle

A simpler and more cost-effective implementation of Grandfather-Father-Son is called the Six Cartridge Weekly Backup. Perfect for small businesses, this backup principle requires daily backups and a single weekly off-site backup copy to provide a data history of up to two weeks. Friday backups are full backups. Monday through Thursday backups are incremental. Here are the steps:

  1. Label each of six cartridges with FRI 1, FRI 2, MON, TUE, WED, THU.
  2. Start the cycle on a Friday and backup the entire hard disk onto cartridge FRI 1.
  3. On Monday, take the MON cartridge and back up only the files that have been created or modified since the last backup (FRI 1).  This is an incremental back up and should be stored on-site. (A full backup, rather than incremental, can be used, if desired).
  4. Repeat Step 3 on Tuesday, Wednesday, and Thursday, using corresponding data cartridges.
  5. On Friday, take data cartridge FRI 2, and perform a full backup.  You have just completed a full rotation of the weekly principle. Again, be sure to store this data cartridge off-site.
  6. The weekly process continues by repeating Step 3 and Step 4 using the same MON, TUE, WED, THU data cartridges.  Step 5 is implemented by alternating cartridges FRI 1 and FRI 2.

An illustration of the Six-Cartridge Weekly Backup Principle is located below.


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