Backup Hardware Options

In the course of the software reviews, I used a broad range of SCSI-basedtape devices. Some of these devices are appropriate for workstation use, whereasothers are better suited for enterprise-scale backup servers. The specificdevices I used included:

DAT refers to a basic 4mm tape design, but these DAT tapes are not digitalaudio tapes, despite the name. They adhere to Digital Data Storage (DDS)standards, which currently include DDS-1 and DDS-2 specifications (DDS-3 isscheduled for release this spring). The primary difference between them iscapacity (90-meter maximum for DDS-1 and 120-meter maximum for DDS-2). Inaddition, DDS-2 supports better compression schemes than DDS-1 and thus hasadditional storage capabilities.

QIC standards are for quarter-inch tapes and represent an inexpensive drivedesign. Currently, the Conner 3200 is one of the few available. This drive doesnot support compression in Windows NT and is viable only for workstationbackups.

Digital Linear Tape (DLT) represents a major advance in tape constructionand longevity. These tapes can withstand 500,000 passes through a tape drive andhave a shelf life of 10 years, which far exceeds 4mm and 8mm designs. Inaddition, these drives offer large amounts of storage (10GB to 40GB), use adual-channel read/write head, and support Digital Lempel-Ziv data compression.These features allow excellent data streaming (where data-in rate speed matchesthe drive speed, so fewer stop/start interrupts occur). Quantum currently makesall DLT engines.

Because of their high costs, 8mm tape devices are typically only inhigh-end LAN environments. However, this situation is changing because Exabytehas introduced a packaged system (the 8700) that includes an 8505 tape drive, aSCSI card (Adaptec 1505), all necessary cabling, and a CD with Seagate's BackupExec for less than $3000. The advantage of 8mm drives is capacity: Withreasonable compression, a single tape can hold about 10GB of data.

Performance
These tape drives can be divided into three basic performance categories:

This group includes the Conner 3200, the Archive Python, and the Sony 5200.In my experience, none of these drives supports hardware compression well in NT.The Python offers it, but without decent compression or speed. The Conner 3200and the Sony 5200 work best for files that don't compress well, such as photo CDimages and small C++ files. The average capacity of these units is 2GB, with abackup speed of 15MB-per-minute (MBpm) to 30MBpm, depending on your PC's speedand configuration. In my opinion, these drives are only for workstations. Theprices are much less than $1000.

The drives in this group are the Exabyte 8505/8700 and the HP C1533a. Theyboth offer 4GB to 10GB of real storage and have backup rates of 30MBpm to45MBpm, depending on PC speed and data type. An interesting side effect is thatthese drives don't stream tapes, so disruptive events don't bother the drives'performance much. In other words, using two of these devices doesn'tsignificantly slow either device. Group 2 pricing ranges from less than $1000 to$4000. All the listed devices can easily handle most stand-alone PCs and smallLANs.

This group consists of high-end devices that offer large tape capacities orinclude an autochanger. The Exabyte 210, Qualstar 4220, and Quantum DLT 4000 areall in this group. The DLT4000 is rapidly becoming the standard for largedatabase backups.

Performance Optimization
It is always important to keep the backup devices as separate fromhigh-speed drives as you can. Use separate controllers if at all possible. Thisapproach isolates system I/Os and optimizes speed and efficiency. For example,in my test environment, I have the backup units on the external bus of amultiplexing SCSI controller (an Adaptec 3940). The NT swap file is on afast/wide SCSI drive controlled by an Adaptec 2940, and the NT applications areon a different drive that this same controller handles.

Reducing the Human Factor
One of the most expensive (and error prone) aspects of backups is thenecessity for human intervention. Changing tapes can be a hassle. That's wherean autochanger comes in. An autochanger typically can handle the weekly ormonthly backup requirements of most networks, assuming you use standard rotationschemes. When you couple an autochanger with a fast, high-capacity tape drive,the resulting device can sustain very high throughputs (e.g., 10 to 20GB perhour).

Another automation technology to consider is bar code reading. Several tapedevices, including the Exabyte 210, have built-in readers that let them scan atape label to determine the tape format and usage. When combined with anautochanger, this capability lets the backup software review which tapes areavailable for the current backup application. Some backup software, such asNetWorker, also provides utility functions to generate bar code labels.

Tape Formats
Often, users express concern about tape formats. Because the softwareproducts I reviewed operate in the native, 32-bit NT environment, you mightexpect most of them to support the Microsoft tape format In reality, there hasbeen little acceptance for the Microsoft format outside Microsoft's own productsand Seagate's Backup Exec. For example, Seagate's Backup Director uses an ANSIstandard, and Legato's NetWorker uses Legato's OpenTape format. As it standstoday, there is no clear winner when it comes to tape format.