Tape Or Disk For Backup and Data Recovery?

Data backup and archiving can be a waking nightmare, how best to balance the demands for instant access against the equally important need for security and reliance? Loss of data is one of those events that can quickly turn the IT Professional’s life from one where they receive plaudits for how well the systems are running to one where their whole career might be under threat.

What is the best system to use? Are disk based easy access systems a better option than tapes and tape libraries, or are the more traditional data backup and hard drive recovery methods a better bet for long term data security? Each technology has its exponents and its detractors. Tape is seen by many as slow and inflexible whereas disk based systems give a convenient, easy to operate, backup system with the ability to add on extra features such as de-duplication that require a dynamic filing system.

Add to this the current cost of hard disks, a 1.5TB disk does not cost that much more than a 1.6TB LTO 4 tape, and the tape capacity is based upon average data compressibility, the native capacity is 800GB, and disk is not the expensive cousin any longer. So does this mean that tape is going the way of the Dodo and that the future is disk based? The question to ask is “what is the purpose of our backup system”.

Is it convenience?

A system that is easy to use and to manage is operationally a better bet than one that is cumbersome or complicated. It also means that data does get backed up, even the most robust method falls apart if no one uses it. So if you have users with laptops who can quickly kick off a backup via the internet with no real effort, then it will happen and you are significantly less likely to find your self at the mercy of a data recovery company.

Is it manageable?

The downside to ease of use is overuse and abuse. Make life too easy for people and they will back everything up without any thought and you end up with a nightmare. Get the policies right though and all should be well. With a dynamic filing system you can implement de-duplication and single instance-storage so that the actual space requirement is minimised.

Does it provide business continuity?

Again, in most instances the disk-based system can win over the other options, data is effectively on-line, or at least near-line. The act of restoring data following an accidental deletion of a corruption is not too arduous, and should not involve several days nagging the IT department before the data is back in place.

So, get rid of the tape storage?

Not so fast. The on-line backup, and the clever sophisticated disk based store might give you convenience and an immediate result when there are minor problems but what if the problems are more severe or the requirement for data is external, for example related to banking regulation or some other aspect of compliance?

Disaster Recovery

The overhead of getting the tapes, cataloguing them and restoring the required data, seems less of an ordeal when there is a total system failure or a wipeout, for example following a fire or a flood. The fact that you can send for the backup tapes from off-site storage and get up and running again is all that matters. Even when the on-site backup tapes have been submerged under a few feet of water, the chances of a full data recovery are good, far better than those for any disk, especially one that was still spinning when the flood came.

Where issues of regulatory compliance arise being able to take a set of tapes that provide a snapshot of the systems at the required point of time is a major boon. No question that the live data may have been tampered with, or that a snapshot from the near-line system may have been inadvertently deleted, the month end tapes for the required time will have been sitting keeping a copy of the data nice and secure, and with a lower power requirement than an always-on system. If you have taken the chance to use the WORM feature of some of the tape systems such as LTO or T10000 then this confidence can be enhanced further.

Data Recovery from Tapes and Disks

Record some data to a tape and then to a hard disk drive. Take each and drop them from six foot of the ground, then try recovering the data. The disk might work if you are very lucky, the tape will almost certainly work. At worst the tape casing will required a bit of work to but generally it will be fine. As a data recovery specialist I know which I would rather have my backup archive stored on in the event of an impact, it would be the tape every time.

The point is that the two data storage media are different, and designed for differing purposes. Disk based systems give convenience, fast response and can be an invaluable near-line backup system that will smooth out the delays that could otherwise be caused by minor operating glitches. Tape based systems, however, give a solid backstop of data security and a reliable data audit trail.

The answer to “tape or disk?” is ideally “both”. The rather cumbersomely named D2D2T (disk-to-disk-to-tape) systems provide a hybrid of both technologies making use of the speed and flexibility of disk for immediate backup and recovery, but with the robust backing of tape storage to add that extra level of security.


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