This is a note from Ecrix Technical Support to let you know what can be done to address excessive SCSI noise issues that affect some VXA tape drive users in a Mac environment, and what you can do to reduce SCSI noise if you're affected.

EXPLANATION:
Some combinations of host computer, SCSI controller card, cabling and termination setup, and external sCSI devices can cause excessive noise in the SCSI channel. This type of situation affects only a small percentage of VXA users, and it is not unique to VXA drives. Many other types of high performance SCSI devices can be affected. Macs in particular are susceptible to noise with external SCSI devices, because of the high quality internal grounding of the Mac box, which makes external devices more sensitive to noise. In most cases, it is easy to reduce the SCSI noise level to allow for proper functioning of the drive.

MANIFESTATIONS:
Some of the things you might see if your SCSI noise level is excessive are slow read performance, frequent lighting of the cleaning LED, and occasional write errors. Sometimes you'll see Retrospect errors 203, 206, 205, or 100, and/or reports by Retrospect of dirty heads, and/or bad media.

POSSIBLE CAUSES:
Some of the things that can cause the excessive SCSI noise:

a. A SCSI Low Voltage Differential (LVD) drive is being used with a Single Ended (SE) SCSI controller. For example, some early G3s came with a SE wide controller. Because of the cable length limitations for SE Wide SCSI, you cannot connect a drive externally to this controller. This is documented on the Apple website at http://til.info.apple.com/techinfo.nsf/artnum/n24330

b. The cables you're using with your SCSI-2/SE  controller have insufficient shielding or exceed the maximum allowed with the SCSI-2 specification, which is 9 feet (3 meters). If you exceed this length limit you may get excessive noise and random errors.

c. Improper termination can also cause excessive noise and random errors.

d. SCSI noise causes older versions of the VXA drive firmware to report that the drive needs to be cleaned. This has been fixed in VXA firmware versions 2524 and higher.

e. These are the most common causes which apply to most situations. Other causes can be present sometimes.

SUGGESTED FIXES:
In most cases, these easy fixes can reduce the SCSI noise level to allow for proper functioning of the VXA drive.

a. If your cable length exceeds the SCSI-2 specification, replace your cables with shorter cables, and make sure that your cables have proper shielding.

b. Make sure that you have proper termination and that your terminator is of sufficient quality.

c. In some cases, you may need to install an additional SCSI controller card for the VXA tape drive and other external SCSI devices. (e.g. if you have an early G3 with built-in wide SCSI controller).

d. Make sure that you have the latest version of the VXA firmware. The newest release (v. 2736) is due out next week. Among other things, it will also prevent some incidences of 203 errors. The firmware is available for download from http://www.vxa.com/support, and can be installed with the Mac version of VXAtool, also available for download.

e. If you are still experiencing issues please contact Ecrix's support department at 1.877.vxa.tape (1.877.892.8273) or at [EMAIL PROTECTED] >From outside the US you can call 1.303.402.9262. All of our technical support engineers have the latest information on these issues and will be happy to work with you.

--
Frank Saab
[EMAIL PROTECTED]
Ecrix

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