Cheap disks and smoking bandwidth have changed the face of backup. In tandem with evolving technologies like de-duplication and more efficient use of VTLs, backup is hot. We explore new approaches to data archiving that won't bust your budget.

For most of the past 20 years, making backups has involved a potentially incendiary combination of tedium and little opportunity for reward, plus high career risk if things go south. The only variation to this routine occurs when vendors try to get us excited with new versions of the same backup software or bigger, faster tape drives. Year after year we back up from disk to tape, and when it comes time to restore, we search for the right tapes. Whoopee.          
 
But now, two trends have combined to bring big changes to backup technology. Vastly decreased costs for both disk drives and bandwidth make it worthwhile to reconsider your backup setup. It might be a pain in the neck, but maturing technologies, such as VTLs (Virtual Tape Libraries), and increasingly intelligent backup software have "evolutionized" corporate backup.

The first trend is the free fall in the cost of high-capacity ATA and SATA disk drives and arrays. Keeping a gigabyte of data on disk once cost 10 times as much as storing the same data near-line in a tape library. Since disk costs have fallen faster than tape costs, the difference in now less than 5-to-1.

Not only are SATA drives much less expensive than the Fibre Channel and SCSI drives used to host high-performance applications, the sequential nature of writing backups to disk plays to their strengths. High-performance drives have intelligent-command queuing, shorter settle times and higher rotation speeds that accelerate the kind of random I/O a database performs. But the capacity-optimized SATA drives can handle sequential I/O just as well as their pricier cousins.

The second change is that as quickly as disk space costs have fallen, so have bandwidth costs. The industry frenzy to lay more and more fiber across the world in the 1990s created a bandwidth glut that's made multi-megabit connections affordable even for residential use.

The challenge we face as system managers is to figure out which technologies, like backup to disk, are really sea changes, and which ones, like server-less backup across the SAN, will turn out to be a great idea on paper but a bust in real life.

The most obvious impact of falling disk prices has been the rapid adoption of disk-to-disk backup. Most system managers change from tape to disk as their primary backup medium to speed up their backups. Unless they're still using DLT8000 drives, they soon discover that the speed of the tape drives isn't the limiting factor in how fast most of their backups run.

Backing up to disk lets you back up more data in the same amount of time not so much by accepting data faster, but by letting more backups run in parallel. Unless it's multiplexing, which has its own problems (see "Backup Technologies Past"), a backup application can send only one stream of data to a tape drive at a time. Because tape drives in libraries are expensive, the number of drives available limits the number of backups most organizations can run in parallel.

Modern tape drives have a voracious appetite for data. They move tape at 120 inches per second and ingest data at up to 120 MBps. If a backup stream can't keep the drive fed, it must stop the tape, rewind past the point where it left off and start recording again. Not only does this increase the wear and tear on the tape drive, it also slows down the process significantly.

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