Distinct backup-to-disk architectures emerge

As database volumes grow larger, backing up data to disk, rather than tape, is gaining favor among life science companies. Now, as the backup-to-disk field develops, companies are finding that there are a couple of approaches that may be taken, each with different costs, benefits and trade-offs.

Discussion of the various backup-to-disk approaches was the focus of a recent talk by W. Curtis Preston, president and CEO of the consulting firm The Storage Group. Preston's talk, titled "Integrating Disk into Backup for Faster Restores," was delivered at the Storage Decisions conference held in New York last week.

"Tape backups are not cutting it," Preston said. He noted that many are finding it takes too long to perform backups and to restore files when dealing with larger and larger databases.

For example, Beyond Genomics Inc. found that as its database grew, tape backups were exceeding their 48 hour, weekend window allocated to perform such tasks.

Additionally, companies are often not following good business continuance/disaster recovery practices of making a copy of each tape to store off-site. "Tape-to-tape copying takes [a long] time, so companies are not copying original backups and sending them off site," Preston said.

This point was reinforced by an impromptu poll by Preston. Using a wireless audience response system at the conference, 7% of the attendees said they are not sending anything off-site and 46% are shipping the original tapes off-site without making copies. Less than half (49%) of the attendees said they make copies of original backups and send a copy off-site.

The traditional solution to deal with both the increasing time to perform a backup and the need to make copies of tapes for safe off-site storage has been to add tape drives. By adding tape systems, backup can be spread over multiple tape drives increasing the aggregate throughput and thus, shortening the time required to perform a backup operation. Such additional drives can also be used to make copies of original backup tapes.

This solution is not cheap since it means buying more tape systems and results in many tape drives sitting idle when backups are not being performed. Many companies have increased the capacity of their tape systems to the point where they simply are not efficiently using them.

Enter backup-to-disk

For these reasons, backup-to-disk is getting closer scrutiny in many life science companies today.

As IT managers look at the backup-to-disk alternatives, two distinct architectures are emerging, Preston said. Both have similar physical configurations that involve backing up essential data stored on high-performance disk-based systems to a secondary disk-based system, which then connects to tape drives.

In one scenario, the secondary storage system acts as a cache that holds the backed up data until it is written to a tape. In this scenario, most restores are done from tapes. And the data on the secondary storage system might only reside on disk until it is backed up to tape.

This approach to backup has a couple of benefits. First, the secondary disk-based storage system doesn't have to be enormous since the system only holds data until it is put on tape.

Second, in contrast to backing up data directly to tape, this approach buffers the data before it hits the tape drives. So rather than streaming data to multiple tape drives (which is the common technique used today) to get a higher aggregate throughout to meet a backup time window, fewer tape drives might be used.

In the other emerging scenario, all data is backed up to the secondary disk-based system, which is also used to restore any lost data. Tapes are used to backup this secondary storage system and are only used in disaster recovery situations.

One benefit to this approach is that all backed up data is online. Restoring files or data volumes is typically faster with this approach since there is no time lost looking for and fetching the appropriate tape with the copy of the lost data. And restoring a specific file is faster since the data doesn't have to be read sequentially (as is the case with tapes).

This second scenario is in great favor today. At the conference, 75% of the audience preferred this method of backup. But Preston noted "the only issue here is cost." Even when using lower performance disk systems for backup, the cost per gigabyte can be about five times that of tape. However, Preston says that he is starting to see backup-to-disk systems coming to market with lower dollar per GB prices.

One final point was that tape is not going away. While backup-to-disk offers higher performance and faster times for straight backups and restores, Preston said tape will still be used in conjunction with these systems to provide archiving of essential data and to support business continuance/disaster recovery initiatives.

Copyright © 2004 IDG Communications, Inc.

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