Friday, August 29, 2008

Backup

Like insurance, computer backups are the type of item that feel like they 'cost' more than they ever return. This feeling is quickly reversed the instant a backup is put to use, but depending on the shop, backups typically happen a lot more often than restores. There isn't any question backups are a necessity, but the real question are: How and Why.

The "Why" question really refers to selecting the best "How" for a shops situation: Why is this my solution. It involves details like: how much data must be backed up, how often must it be backed up, how fast must it be backed up, how fast must it be available for restoration, where must the backup be stored, etc.

I've ran across a few different "How's" in my career. Some of these involved FC attached libraries, autoloaders, single drives. These are all 'local' backups, where the data was copied to some type of local device and managed locally. There is something to be said for today's modern tape technology - it is soo much better than from 5-7 year ago. Speeds are great, capacities are way up, reliability is significantly better. But - tape is labor intensive, having to be handled, moved offsite, back onsite, sensitive to temperature, etc. Good quality tape drives(LTO and up), either stand alone or inside an autoloader/library are costly for smaller businesses. And when a tape drive decides to start acting up, it is your own worst enemy - writing bad data, eating tapes, failing backups.

In recent years an additional local backup has come into popular use - disk. The plummeting cost of disk drives and sky rocketing capacities have made disk drives a very attractive backup option. There are 3 approaches used with disk backup: 1) Disk replaces tapes. Here backups are written to removable drives and then moved offsite / rotated just like a tape would be. 2) Backups are written to disk first, then tape - known as D-D-T(Disk to Disk to Tape). Here the disk acts as an intermediary(with many benefits). 3) Mirrored remote SAN. This is big business stuff mostly using expensive equipment and network connections to actively mirror live data. It's also more of a disaster recovery / failover solution as it does not preserve historical versions.

Going back to #2 above and the "Many Benefits" part. By putting the disk between the data source and the tape drive several good things happen. First off many backup streams can be written to a disk simultaneously, minimizing jobs having to wait for a tape drive to be free. Secondly because these disks are usually in the backup server or 'near' it, when the data is written to tape from them it can be done much more quickly / smoothly, freeing up even more tape drive time. Thirdly, there are now 2 copies of the backup, always a plus. Lastly, if the data is still on the intermediate disk when a restore is requested, the data can be pulled from the disk instantly versus searching for, loading, and seeking through a tape.

There are too numerous to mention local backup software options. The keys to the proper selection mainly involve: The kinds of data being backup up(database, email, normal files, etc), the type of systems being backed up(Windows, Linux, UNIX, etc), and cost. All reputable softwares should support modern media types, be it tape drives/loaders/libraries, VTLs, or disk drives.

Another option exists that can be attractive in certain situations - online backup. Online backups start with an account on a vendor website, an Internet connection, and a small piece of software on the source systems to be backed up. Often times there are options for the backups to run continuously - capturing all file changes in real-time and transferring them securely online for backup, or scheduled backups that only run at certain times. There are a few immediate cautions with these solutions. 1) Is the Internet connection fast enough to transfer the data efficiently? 2) How is the service charged: per MB transferred/per MB stored/per MB on the source system/etc? 3) What options exist for restoring data, both small files or entire systems? An online backup can be a good match given the right billing structure and a desire for low IT resources.

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