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VXA PERFORMANCE TESTS: The VXA Reality Check
A crucial aspect of understanding a new tape technology is knowing how it performs not
just in a testing lab but
in actual use. In a real-life face-off, the VXA-1 drive
performed at more than twice the transfer rate of DDS-3 and nearly equaled DLT 7000.
The VXA-1 tape drive was recently unveiled at the NetWorld+Interop trade show in
Las Vegas on May 11. For the show, Ecrix arranged a special demonstration of the
capabilities
of the VXA-1 in a head-to-head comparison with a Hewlett Packard DDS-3 and a
Quantum DLT 7000. This unique face-off was
dubbed “The VXA Reality Check.”
The Contestants
The live demonstrations were run with a Dell Dimension XPS T500 500 MHz host computer
running Computer
Associates’ ARCserveIT 6.61 backup
software with Windows NT 4.0. All three drives used the same 879 MB data set for
more than 250 backup
procedures over the three-day period of the show.
DDS-3 (DAT)
The DDS-3 was chosen for the test because it is a popular and affordable tape drive that
is typically used by small to medium-sized businesses and workgroups.
A DDS-3 drive offers 24 Gbytes of capacity and a transfer
rate of 2 MB/sec.* Its street price is about $800.
DLT 7000
The DLT 7000 was chosen because of its popularity as a high-performing tape
drive for
enterprise-level operations. A DLT 7000 drive offers 70 Gbytes of capacity and a
transfer rate of 10 MB/sec.* Its street
price is about $4,600.
VXA-1
The VXA-1 is focused on the ability to restore data, and is based on Ecrix's new VXA tape
technology. A VXA-1 drive offers 66
Gbytes of capacity and a transfer rate of 6 MB/sec.* The estimated street price for
a VXA-1 drive is $849.
“Real World” Performance
Anyone who backs up to tape on a regular basis knows that “real world” transfer rates are
typically slower than the stated specifications.
This is usually caused by bottlenecks either at
the system level (which could be attributed to the CPU, the disk drive, or the network)
or at the tape drive level.
System Bottleneck
A system bottleneck means that data arrives at the tape drive at a rate slower than
the drive's optimal speed.
This is what happened with the VXA-1 and the DLT 7000: Both drives
were "starved" for data. With the DLT 7000, this caused backhitching, the repeated
back-and-forth motion of the tape which leads to undue wear on the tape and on the drive
mechanism. However, the VXA-1 adjusted to the system's transfer rate by exploiting its
"Ready Mode," which allows it to accept data at any incoming rate without ever having
to reverse direction. Video footage of both backhitching and "Ready Mode" is available
for viewing in this website's VXA Technology Tour.
Tape Drive Bottleneck
By contrast, a drive-level bottleneck occurs when the system
transfers data faster than the drive.
The DDS-3 drive was unable to keep up with the system's data rate, which
resulted in the drive being the bottleneck.
Optimizing Performance
Tape drive performance is affected by a multitude of factors. Changing the system
conditions will lead to different performance from the drive. The system configuration
used for this test was selected to represent one typical real world situation, with equipment
that is widely used in mid-range enterprise and workgroup settings.
Because of its inherently flexible and reliable design, the VXA-1 drive performs optimally
in a very wide range of system configurations, including the configuration used for this test.
Future issues of this newsletter will explore the effect on performance of factors like
network bandwidth, data compressibility, host computer speed, and so on.
The End Result? The VXA Reality Check
Throughout the tests, the DDS-3 transfer speed averaged 1.6 MB/sec, the
DLT 7000 transfer speed was 3.8 MB/sec, and the VXA-1 transfer speed was 3.5 MB/sec.
The conclusion? In these tests, VXA-1 offers
more than twice the
performance and capacity of a DDS-3 drive at the same price point. VXA-1
performance and capacity are comparable
to DLT 7000 but at only a fraction of the cost.
Test Summary
| Drive | Capacity
(GBytes) | Nominal
Transfer Rate
(MB/sec) | Test
Transfer Rate
(MB/sec) | Price |
| VXA-1 | 66 | 6 | 3.5 | $849 |
| DDS-3 | 25 | 2 | 1.6 | $800 |
| DLT7000 | 70 | 10 | 3.8 | $4600 |
* Specifications assume a 2:1 compression ratio. Compression, capacity and throughput will be dependent upon the type of data and
system configuration.
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