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Pain point of time.

For IT administrators, nothing is more deafening than the ticking of the backup window except perhaps for the protracted silence of a restore.

Today, IT administrators, in particular those charged with the day-to-day responsibility of backup and recovery, face the constant, usually uphill battle of trying to maintain application performance levels, while ensuring that all the data that needs to be backed up is being backed up--and, more importantly, that it is quickly and easily recoverable when needed.

Time--or the lack thereof--has clearly become an IT administrator's worst enemy.

For years, IT administrators have addressed the shrinking backup window and increasing user data requirements by throwing faster, denser tape drives and libraries at the problem, and tape drive and library vendors have responded by regularly introducing products that are more capacity-rich, throughput-intensive, scalable, and cost-efficient than the previous generations of products.

But despite these advancements, the market has taken clear steps over the past couple of years away from tape and toward disk for backup and recovery. In fact, you could argue that the arrival of disk-based backup options for the first time brings recovery--and the concept of recovery windows, or recovery time objectives (RTOs)--into focus.

Restoring data from tape, on the other hand, has notoriously been a slow and painful process, often taking days or weeks to accomplish.

Inherent issues with tape--in particular, issues with data streaming (on the backup side) and multiplexing (on the restore side), as well as ongoing issues with drive and media reliability, and the increasing affordability and availability of SATA-based disk backup options, have led many users recently to re-evaluate their existing backup and recovery procedures and implement disk--either as virtual tape, as a disk backup/recovery target, or as a host-based option.

The increasing popularity and availability of these disk-based backup options has led to a lot of confusion in the market. What are the key differences among them? Which is better? How are they implemented? What type of results can users expect?

While none of the new disk-based backup and recovery technologies mentioned above are perfect, all three, if implemented and used properly, can significantly improve IT administrators' ability to meet--and even shrink--backup and restore windows by allowing them to read and write data faster than it's possible with tape. Of course, this assumes that there are no serious underlying problems with the backup environment.

Recovery speed, in particular, can be notably faster: Data can be accessed directly from disk (assuming the data still resides on disk and has not been archived to tape); it does not have to be "re-assembled" as it would in tape implementations that rely on multiplexing to boost backup performance.

However, the speed at which data can be written and read varies--and often significantly--from product to product and among disk-based backup categories, and is ultimately limited by the speed of the backup application and the storage network. Additionally, there are other potential drawbacks with disk-based backup technologies, including issues with cost, compatibility, integration, and installation--to name a few.

Take disk as a backup/recovery target--or what is now commonly known now as disk-to-disk (D2D) backup. These types of systems are available from a variety of vendors, including EMC, Network Appliance, Nexsan, and StorageTek.

The idea is to take a SATA RAID system, load a file system onto it, connect it to the backup server, and then use either proprietary or backup software applications from leading vendors, depending on which product is implemented, to back up data to the RAID disk target instead of traditional tape.

While this approach is straightforward and does offer significantly faster backup and restore times than traditional tape backup, it requires users to make changes to their existing backup configuration. Additionally, because data is being backed up to disk, not tape or virtual tape (see below), users must contend with the issue of file-system fragmentation, which can significantly affect read and write (i.e., backup and recovery) performance over time as well as the limitations of D2D.

Also, because these systems leverage general file systems, such as UFS, JFS, NFS, and NTFS, users will need to create and manage multiple file systems, as well as the volumes contained within the file systems, as their data volumes increase. Each instance of these file systems is typically limited to 2TB of capacity.

There is also guarded concern that disk that is used as a backup target could represent a potential security breach within the network because of its reliance on standard interfaces, which are known to be penetrable to hackers, viruses, etc.

Another option is host-based disk-to-disk (D2D), which is available from traditional tape-based backup software vendors, such as Atempo, Computer Associates, CommVault, Legato, and Veritas, among others. This option essentially gives users the choice of directing data to SATA disk, to tape, or both, when backing up.

While this type of solution has many advantages, notably its integration with existing backup and restore applications, its ability to execute multiple, simultaneous backup and restore operations to disk and to combine disk snapshots with backup and recovery operations, and to stage data to both disk and tape as needed, there are also some downsides with the approach.

In a nutshell, users are responsible for purchasing and integrating the various components of the host-based D2D implementation (e.g., RAID systems, servers, cables, etc.)--and they must deal with any compatibility issues that arise.

While D2D and host-based D2D options are front and center in the ongoing tape versus disk debate, VTL solutions from vendors such as Alacritus, Diligent, IBM, Quantum, SEPATON, and StorageTek are also becoming increasingly popular among users because of their ability to boost backup and restore performance with virtually none of the side effects of the other approaches.

In fact, some analysts believe--and users will confirm--that VTL offers the best of both tape and disk rolled up into one nice, neat plug-and-play appliance.

VTL solutions "trick" the backup server into thinking it is still backing up to tape, though the target is now SATA disk. VTLs generally slip into the existing backup environment unnoticed and work with traditional backup applications to expedite the backup and restore process.

What makes these systems potentially better performers than other D2D options is the way they "capture" data. Unlike D2D systems, which rely upon native OS file systems, virtual tape libraries write data to proprietary file systems and present the data as physical tapes to the backup servers. This not only means VTLs have the same media management capabilities (e.g., cataloguing, media expiration, etc.) as tape systems but also that they have none of the file-system-imposed performance limitations of D2D options.

Some VTL systems also allow users to further improve performance, reducing the backup window and better meet recovery time objectives by adding additional Fibre Channel connections as data demands change. If higher performance is required, users simply enable additional connections. Because the target is disk, not tape, there is no shoeshine effect.

For a further performance boost, vendors also offer a "synthetic full" backup feature. This is typically a very CPU and I/O intensive application requiring very robust servers and backup infrastructure. Alternatively, the VTL can use a system of "pointers" to keep track of data as it changes. In addition to providing a "map" or a "link" to the actual data residing on the VTL, the pointers work in conjunction with a database that contains information about the data (e.g., the type of data, performance requirements, security requirements, etc.) that is being backed up.

Instead of physically copying changes during synthetic full creation--as other vendor products do--new and changed files are marked with pointers, which can then be used to quickly create full backup images.

Capacity use is minimized (synthetic backups consume just 32MB of capacity) and performance is super-fast. Synthetic full backups can be done in just a fraction of the time it typically takes to do a traditional backup to tape, and restores are near-instantaneous. For example, the equivalent of a 100GB LTO tape image can be made in less than 60 seconds; the equivalent of a nine-hour backup in one minute.

And that's just the tip of the iceberg for VTL. Because they run their own file systems, they are also capable of performing a variety of other features, including snapshot real-time replication, and continuous data capture, which combined should make backup and restore windows a thing of the past. Time is no longer a factor.

Jay Livens is channel development manager for SEPATON, Inc. (Marlborough, MA)
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Article Details
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Title Annotation:Disaster Recovery & Backup/Restore
Author:Livens, Jay
Publication:Computer Technology Review
Geographic Code:1USA
Date:Aug 1, 2005
Previous Article:Plugging into utility storage for enterprise-class application servers.
Next Article:Modified time-based servo enables increased track density on tape.

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