Data Recovery Article
Tape Recovery FAQ
By Doug Owens
1. How Many Copies are needed for Tape Backups?
The value of the data should dictate the number of copies, and every organization is different.
If the information is critical to your business, you should have multiple copies. Data that is less essential to the running of your business -- archived customer records, for example -- needs only one copy.
The important question to ask yourself when determining the value of your data is this: If your live data was lost for any reason, what information would you need in order to continue to serve your customers without shutting down your operation for any length of time?
Ultimately, every organization's data is different, but you should have at least one copy of anything if it is worth be backed up in the first place.
That being said, you should test all of the copies: If the tapes aren't being written properly, having 10 copies won't matter because they will all be bad.
2. How long should a tape be in rotation before it is retired?
Most tape vendors have recommended specifications as to how long a tape should be kept in rotation. Most tapes are good for about 500,000 head passes before they will experience any problems.
So, for example, it takes 52 passes for a DLT 7000 to fill a tape, and another 52 passes to verify the backup. Assuming you don't do a restore (which is another 52 passes), you can back up to that tape about 5,000 times.
This is assuming the drive is writing correctly of course. In addition, most people don't take care of their equipment, so it is probably best to replace the tapes ahead of the recommended specs.
If you're doing weekly backups, you probably want to replace the tapes every two years. In the end, it's better to spend the money on new tapes than just as much money to do data recovery on one tape or risk losing information critical to the operation of your business.
3. What are the top three mistakes that are made when configuring a tape library?
One of the big mistakes is not making sure the backup software has permission rights and security privileges to access the servers and/or files that are to be backed up. For example, if the server containing your accounting data has been secured well but the backup software isn't allowed to read it, that critical data will not be backed up. The best approach is to make a checklist of servers, folders and files you need to have backed up regularly, and then verify that your backup software has the appropriate permissions to access the data.
Also, the backup software should be able to address the library properly. If the correct drivers aren't present, the data won't be interpreted properly.
Finally, setting up preventative maintenance and rotation schedules should be done immediately; doing a retrofit as an afterthought is always problematic. If it is not done immediately, it is easy to put off doing it until it is too late.
4. Where can I find MTTF data and repair profiles for tape libraries -- Overland in particular?
Unfortunately, I haven't seen a "one-stop" comparison for libraries in quite some time, so the only real resource would be to examine each of the product's specification sheets and perform the comparison that way. But you may want to consider at a little more than just the MTTF/MTBF.
Regardless of the "time to fail", if a failure does occur, you may want to focus a little more on the time it takes to get back up and running.
According to Michael Peterson of Strategic Research Corporation, "MTBF ratings for tape libraries are no longer a true measurement of reliability when building mission-critical capable network storage solutions. The proof of reliability comes with the supplier's reputation, warranty, and service policies. If you accept the fact that failures happen, the true measurement of reliability is system availability."
5. How do you minimize tape failure?
Tape backup is still the most frequently used backup method for business users because of its cost-effectiveness per megabyte of data, despite the increasing popularity of recordable CDs and DVDs. However, just like any technology, tape drives, backup tapes and tape backup software can fail.
There are ways to minimize the chances of a tape backup's failing in the first place. Here are a few tips:
Verify your backups. Most backup software will automatically do a quick "read-after-write" verification and will offer optional full verification. The latter is both more thorough and more time-consuming, roughly doubling the backup time, but if your files are crucial, it makes sense to do a full verification regularly.
Store one backup tape off site. This will ensure your files are preserved if your site experiences a fire, flood or other disaster. Some companies swap backup tapes with other offices. With some smaller businesses, it often makes sense for one employee to take the backup tape home with him. Another option is using an off-site storage firm that provides fire-protected storage facilities for print and digital media as well as tape.
Store your tapes properly. With backup tapes on site, keep them stored in a stable environment, without extreme temperatures, humidity or electromagnetism. Do not, for instance, store the tapes in a safe on the opposite side of the wall from a large generator, whose electrical fields can wreck havoc with the data on them.
Rotate tapes. Use more than one backup tape. Instead of using the same tape time after time, rotate through multiple tapes. You can use any of a number of different systems for this. With the odd/even system, you use one tape on one day, a second tape the next day, reuse the first tape on day three, and so on. With the five-day rotation system, you use a different tape for each day of the workweek.
Track the "expiry date." Backup tapes are typically rated to be used from 5,000 to 500,000 times, depending on the type of tape. Tape backup software typically will keep track of the tapes, regardless of the rotation system.
Maintain your equipment. Clean your tape backup drive periodically, following directions in its manual regarding frequency. Consider having an authorized maintenance person from the manufacturer of the tape backup drive or from a third-party repair firm check the alignment of the drive every 12 to 18 months. Most businesses just send the drive back to the manufacturer when it begins to have problems, but if a drive has problems, so can the backup tapes.
Do regular checkups. Periodically test the backup tapes and restore procedures. You can, for instance, restore the data on them to a different server or to a different partition or folder on the same server where the original information is stored.
At the end of the day, never assume your back up technology will never fail. It's just as prone to failure as any other technology. Proper maintenance and testing of your tape technology will mean when threats outside your control jeopardize your data, you can turn to your back ups with confidence and get your business running again smoothly.
6. HOW MANY TAPES NEEDED FOR A FULL BACKUP?
If you flip a quarter and it lands "heads" 10 times in a row, what are the odds that it will land "heads" the next time you flip it? 50%. Why? Because there are only two sides to a quarter, and the risk of it landing on tails is 50% each time you flip it. "Each time you flip" it is the key here.
Same thing with the assumption of tape failure. If one in 100 tapes fail, then every tape you use has a 99% chance of not failing.
Here's the general math argument that a lot of people want to use (and we hear it a lot, but that doesn't make it a good argument). The bad argument is that a certain percent of tapes are guaranteed to go bad (risk) per year. And that based upon the number of tapes being used (N number of tapes per full backup, multiplied by X number of tape sets, we'll name this variable "group"), the more tapes in the backup set, the higher the risk. Or in other words:
Risk (1%) * Group (12 tapes) = 12% Risk
That's not the case, because the odds are based on each individual tape. So if you have a 1% risk (one out of 100 tapes is going to go bad), and you are using 12 tapes, then each tape faces the same risk (one out of 100) versus it being a multiple of the group.
What you get with multiple tapes potentially going bad versus one tape going bad, is that you face increased chances per tape. In other words, it's like flipping that coin 12 times. Each time you flip, you have a one in 100 chance of failing. So if you flip once (one tape), you had one chance of failure. If you flip 12 times (12 tapes) you have 12 chances of one in 100 times failure rate.