Determine your tape backup strategy

The full, differential, and incremental backups are all done with the assumption that the system is quiescent! Backing up a file that is actually being written does not necessarily produce a usable backup. The backup is sequential but the file can, at least potentially, be accessed randomly. Suppose the application writes to a part of a file already backed up to tape and then to a part that has not yet been backed up. Restore this backup and what have you got? A file that is potentially inconsistent. If the two write operations were part of the same transaction, what you've got is garbage. Maybe you can salvage it or maybe not.

If it's all you have, you live with it and try to make your backups when nothing else is happening. If your system runs 24x7x365 you need to find something better.

If you have the computer resources and manpower, you could create duplicate sets of backup tapes. This allows one set to be stored off-site, and another to be kept on-site (for quicker restore situations).

The original backup set could be created overnight, and the second backup set could be created during the day on a less powerful computer system using the original backups as the input source.

We also 'roll-up' our data. If we create daily data files, we backup them up daily, but when we consolidate them into a weekly file, the weekly file is backed-up and the daily backups become free. This same technique can be used to roll-up data for monthly and yearly purposes. This actually saves us quite a few tapes during the year. We use 8 daily tapes, 5 weekly tapes, 13 monthly tapes, and 10 yearly tapes. Granted the files on the tapes become larger, but the frequecy of access is much less for yearly tapes, than for daily/weekly tapes.

My 2 cents.

For our web hosting cluster whit about 350 GB Diskspace we have a backup scheme with full backups every 14 days and various levels of incremental in between. So for a restore we need in any case a maximum of 5 storage sets (full, level5, level 3 and max 2 incremental). We are using Solstice Disk Suite (Legato Netwoker) and a 21 Slot DLT8000 library so the scheduling is not much a hassle, I have just to change tapes every 14 Days.

The changed tapes are stored in another building across a big street and two railway tracks. As long as we don't have a huge bomb or a big earthquake either the tapes or the data will survive.
But I stumbled over another very important issue, TEST YOUR BACKUP OFTEN. I installed the Software, made a backup and restored it, worked fine, so nothing more to do I thought.

After two months I had to install a bigger disk in my personal workstation, so I decided to test my backup and perform a disaster recovery. I made a full backup during one night, the next day I exchanged the disks installed the software in order to recover and started the recover procedure. But the backup software was not able to find my savesets on the tapes.

A longer investigation showed that we had only the last saveset on each tape, due to a configuration error the tape rewound before each new saveset (a saveset is a tape file which contains all files in a given backup from one partition of one machine).

Well I installed the old disk again and had my data back again, but I don't dare to think about what would happen if I only discovered this problem while performing a disaster recover of the productive web server farm after a real disaster..............................

Having done a few Disaster Recoveries over the last 25 years, I firmly believe that full backups every night are the best way, if you can. Recovery from incremental/partial backups is slower, and being more complex, adds the element of human error. I usually set up backups for Mon-Thu, Fri 1-4 (Friday of the Month), Jan-Dec, and the December tape is kept forever.
This makes DR and file recovery easy.

Graeme Cooper

We do full backups every night on our 7 servers. Incremental backups proved too tedious to restore from. We use 2 backup units - a DLT and an older DAT drive so that the jobs finish no later than 8am. The backups are verified every night as part of the scheduled backup job. Random restores are performed on occasion to check tape integrity.

Tapes younger than 60 days are transported to and from the office every day as needed (if not needed, they are stored in my house). After 60 days, backup tapes are written over except for a weekly Friday tape that is sent off-site to a climate controlled vault in a storage center for permanent retention.

Older backup units are also retained so older tapes can be restored if needed.