Testing Tape Susceptibility To Dust.

This article is the second in a two-part series. The first part appeared in the April issue (QI 2000) of Storage Inc.

Prior to testing, NTS*XXCAL Test Engineers developed a test script using Rational Visual Test v 4.0r to perform backup, appends, and restores of ELA-TIA files. These are the standard EIA-TIA (Electronics Industry Association/Telecommunications Industries Association) TSB-38 files designed for testing modem hardware. There are five files, each with a varying degree of compressibility. The content of the files makes them valid (Table 1).

General Procedures

* Setup Server Platforms: NTS*XXCAL Test Engineers set up four server platforms with Microsoft Windows NT Server v4.0 for testing. For details on server configuration, see Table 2. Each server platform was configured with one of each of the tape drives under test (i.e. server #1 was configured with a Tandberg SLR24 Tape Drive, server #2 was configured with SLR50 Tape Drive, server #3 was configured with a Sony DDS4, etc.). NTS*XXCAL Test Engineers, then, installed appropriate drivers for use under the Microsoft Windows NT operating system.

* Installation: NTS*XXCAL Test Engineers, then, installed Seagate Backup Exec for NT v7.2 onto each of the server platforms and verified that the platforms were still functioning properly prior to proceeding.

* Benchmark: The tape drives were operated in a continuous backup/restore mode and the required dust concentration began. The backup/restore functions were restarted every 1.5 to 2.5 hours (after one full backup or restore) depending on the drive speed for a standard 8-hour day. These conditions were maintained for six days.

a. NTS*XXCAL backed up a tape cartridge fully using EIA-TIA files. (Note: During backup, NTS*XXCAL would back up the tape cartridge fully if the tape cartridge was equal to or less than the server hard drive capacity; otherwise, NTS*XXCAL performed append backups until the tape cartridge was full.)

b. Once the tape cartridge was full, NTS*XXCAL attempted to restore the tape cartridge onto the hard drive.

c. NTS*XXCAL erased the tape and repeated from step a. until the test either failed or 144 hour of testing has been performed.

Test Result Summary: Linear Recording Drives

* Tandberg Data SLR24

144 hours: Test completed. No functional problems experienced during test.

* Tandberg Data SLR50

144 hours: Test completed. No functional problems experienced during test.

Test Result Summary: Helical Scan Drives

* DDS3, HP Surestore 24i

8 hours 14 minutes: Backup operation failed. Drive cleaned and restarted.

84 hours: Restore operation failed. Drive cleaned and restarted with new tape.

144 hours: Test completed. Two failure incidents during test.

* DDS4, Sony SDT-l0000ME, drive no. 1

21 hours 40 minutes: Backup operation failed. Drive cleaned, but is unable to continue test. Drive replaced.

* DDS4, Sony SDT-10000ME, drive no. 2

25 hours 11 minutes: Restore operation failed. Drive cleaned and restarted.

34 hours 11 minutes: Restore operation failed. Drive cleaned but is unable to continue test. Test terminated.

Conclusions

After being exposed to dust sedimentation equivalent to 10 years of operation in an office environment, the linear drives operated flawlessly throughout the test, while helical scan-based DDS drives experienced severe operational problems, ranging from the need for head cleaning to unrecoverable hardware failure. The test at NTS*XXCAL has shown that when it comes to a tape drive's ability to withstand its most common enemy-the adverse effect from dust and particle debris-tape drives based on Linear Recording show much better results than tape drives based on Helical Scan technology. The reason for this is one or several of the following factors:

* Linear Recording tape drives have a much less complex mechanical design than their helical scan counterparts. Basically, this means that there are fewer parts that can be affected by dust, hence fewer parts that can fail.

* Linear Recording tape cartridges contain the magnetic tape itself inside the cartridge at all times. Only a small door in the cartridge shell allows the magnetic recording head to make contact with the magnetic media. This results in less exposure of the magnetic tape to the dusty environment, which again reduces the risk of media failure due to dust.

* Helical Scan media, on the other hand, is pulled out of the cartridge shell, then led through a complicated system of guides and capstan rollers before being wrapped around a rotating head. This means that a large portion of the magnetic tape is exposed to the dusty environment as soon as it is loaded into the drive causing the problem described in Table 3.

In short, it is a fact of life that dust will appear everywhere in our everyday life and we expect tape backup drives to operate in that same environment without any problems. This test has shown that, when it comes to handling the adverse effects of dust in the environment, Linear Recording tape drives have far better capabilities than comparable Helical Scan tape drives.

A Word Of Caution

As this test has shown, linear recording SLR tape drives are able to operate properly while being subjected to an environment that creates operational failure in helical scan drives. Even though the Tandberg Data tape drives were able to operate in a very dusty environment without any problems, this should not lead to the conclusion that normal preventive maintenance can be ignored. All tape drives should have their read/write heads cleaned periodically according to product specification to prevent unnecessary performance loss.

Runar Angelsen is the product manager of media at Tandberg Data ASA (Oslo, Norway).

                         TSB-38 File Descriptions
File   Details                      Comments
1. TST Number-only file signature   Typical of a vector drawing file
                                    (CAD).
2. TST WordPerfect document
3. TST Portion of an executable for .EXE file
       x86 processors
4. TST 64-bit random data           Typical of a .ZIP
                                    (or other compressed) file.
5. TST Mixed
                          Test platform hardware
                               and software
Platform Name    Dell Optiplex GX1
Processor        Intel Pentium 11/400 Mhz
System Memory    192 MB
Operating System Microsoft Windows NT 4 Server with
                 Service Pack 5
SCSI Adapter     Adaptec AHA-2940UW Ultra Wide
Hard Disks       Seagate 5T19171N SCSI hard drive (2 unit),
                 Maxtor 90640D4 IDE hard drive (1 unit)
Backup Software  Seagate Backup Exec for Windows NT v7.2