ADOBE's SCSI troubleshoot guide
T e c h n i c a l S u p p o r t SCSI
The most common technical support issues are listed on this site. Additional issues will be added as needed to improve our service.
SCSI Technical Support Index
1. Cannot access all AV SCSI drives connected to system
2. Jaz drive on SCSI chain caused video buffer underrun error
3. No AV hard drives were found on boot up
4. Problem connecting SCSI drives to Fibre Channel controller
5. Connecting single ended SCSI devices to an LVD SCSI bus
I moved my nonlinear editor to another room and reconnected everything as it was before, but now 3 of my 8 AV SCSI drives can't be accessed.
Such behavior is a problem with SCSI and is easy to resolve. Check for proper SCSI termination. On external hard drives, the SCSI terminator must be attached to the connector at the end of the chain. Without proper SCSI termination, all types of strange SCSI behavior can occur, including missing drives and system lock ups. If the termination used is provided by the last hard drive in the chain by setting a jumper, check that the terminated drive is the last one in the SCSI chain. Also, check that the proper type of terminator is being used. An LVD SCSI terminator cannot be used on single-ended SCSI, unless it is switchable, and vice versa. However, an LVD SCSI terminator can be used on an Ultra2 LVD SCSI chain with mixed LVD and single-ended SCSI devices.
The next issue to check is proper cabling. Be sure the SCSI cable is properly and securely fastened to the connector on the back of the drive enclosure. Since it is possible to bend the pins on 68-pin connectors, check each connector to be sure a pin is not bent. It is possible to carefully use a pair of needle-nosed pliers to straighten a bent pin without breaking it.
I added a Jaz drive to the end of the Ultra2 SCSI chain connected to my Avid system, but when I tried to digitize at 300 kb/frame I got a buffer under run error. Why?
All forms of SCSI have to arbitrate the SCSI bus to accommodate the speed of all devices connected to each SCSI chain. While it is true that Ultra2 SCSI supports up to 80 MB/second, it also has to support a 10 or 20 MB/second device by dropping the speed of the entire daisy chain to the speed of the slowest device, which in this case is the Jaz drive. Actually, you're fortunate the drives are working at all, considering that all 68-lines are not being properly terminated.
Anytime a 68-pin to 50-pin adapter is used, termination becomes an issue. This is why people normally connect a 50-pin adapter to a middle connector on a 68-conductor cable. But even in such cases, the speed of the bus reverts to the slowest device on the chain. You should not mix Ultra2 LVD SCSI devices with single ended SCSI devices on the same chain, if you want maximum performance out of the Ultra2 devices.
Remove the Jaz drive and connect it to another SCSI adapter or to a 50-pin connector on the SCSI adapter, if it has one. This may require use of an internal Jaz drive or a special cable from the SCSI adapter manufacturer to convert an internal cable to an external cable.
I turned my editing system on and none of the AV drives were found. Help!
The most common cause of this is turning on the SCSI hard drives after the machine has started to boot. Since the drives were not yet ready when the SCSI adapter began to scan the bus, the drives were not found. Shut down the system and restart it, but always turn on the external hard drives first and wait a few seconds before starting the system.
Other causes are a disconnected cable, a defective cable, or a defective or missing SCSI terminator. The worst case scenario is that the disk configuration was lost in Windows NT. In such a case, the only easy way to restore striped drives is by restoring the configuration information from a backup. There is a utility on the Windows NT Resource Kit CD-ROM that may enable you to regenerate the striped sets, but you have to know the partition information and which drives were striped together.
We have found that the prime use for the FTDISK utility is to remove a mythical striped set from Disk Administrator. Such a mythical stripe set may remain when a set of striped drives are removed from the system without first deleting the stripe set from Disk Administrator.
Another possibility is insufficient termination power. Normally the SCSI host adapter supplies termination power to the SCSI bus but there are occasions when the power is insufficient. When termination power is too low, the SCSI terminator at the end of the SCSI chain is incapable of raising the voltage into the normal range. In such cases, the drives may not appear on the chain during the POST (Power On Self Test) stage of a computer restart or may appear intermittently. The solution is to check the termination setting in the SCSI host adapter BIOS. It is normally set to Automatic. Then remove the SCSI drives on that chain and check whether the jumpers on the drives are set to provide termination power (TP) to the SCSI bus or to let the SCSI bus provide termination power. Setting the jumper on at least one of the drives to provide termination power to the SCSI bus should eliminate termination power issues. If the drives are removable, then all the drives should be set to provide termination power to the SCSI bus.
Note: SCA type single-connector drives (normally removable) do not support termination power jumpers. In such cases, setting termination power at the drive is a non-issue and other causes must be considered as mentioned above.
I was told that I could use SCSI drives with my Fibre Channel adapter, but when I tried to connect them, the connector wouldn't fit. Do I need a special adapter?
SCSI drives and devices can be used with a Fibre Channel host adapter but only with a Fibre Channel to SCSI bridge adapter, which is a special controller that converts a Fibre Channel bus to SCSI bus. The only other way to connect SCSI drives or SCSI devices, such as a tape drive, to a Fibre Channel host adapter is with a Fibre Channel RAID controller that has SCSI drive channels. Fibre Channel does support the SCSI protocol. In fact, Fibre Channel doesn't care what protocol is being used. But in answer to your question, there is no way to directly connect SCSI drives to a Fibre Channel host adapter. It is important to remember that SCSI hard drives must not have conflicting SCSI ID addresses. Since Fibre Channel doesn't use such hard-wired addresses, it does not experience such a problem.
Connecting single ended SCSI devices to an LVD SCSI bus
LVD SCSI includes Ultra2 SCSI, Ultra160 SCSI, Ultra160/m SCSI, and upcoming Ultra4 SCSI. These SCSI buses utilize 68-conductor cable but are backward compatible to single ended SCSI devices, even those such as narrow SCSI with 50-pin connectors. You cannot use high voltage differential SCSI devices, however, due to over driving the LVD controller chips.
In general, single ended SCSI devices should not be mixed on an LVD SCSI bus, because the entire bus reverts to the speed, cable length, and device number limitations of the single ended SCSI standard. In addition, the 16-bit high data byte must be terminated at the end of the chain. There are pass-through terminators that terminate the high byte for 16-bit SCSI and LVD SCSI and allow 8-bit SCSI devices (50-pin) to be connected at the end of the chain. But the best solution is to not mix single ended SCSI devices on the same bus as LVD SCSI devices. If there is no other alternative, limit narrow SCSI devices to no more than two such devices on the bus.
LVD SCSI host bus adapters that have a separate 50-pin connector for narrow 8-bit SCSI devices make it possible to mix both types of devices on a single controller, with maximum performance of both types of SCSI devices.
When mixing Ultra2 LVD or Ultra160 (Ultra3) SCSI devices on a single ended Ultra SCSI but, the LVD SCSI devices will operate at the speed of the Ultra SCSI but, which is a maximum of 40 MB/second. Since the LVD devices are not terminated, it is imperative that an active terminator be attached at the end of the cable. Additionally, an Ultra160 SCSI device connected to an Ultra2 SCSI bus will revert to the 80 MB/second maximum speed of the Ultra2 bus. Remember that a single hard drive, due to its mechanical limitations is incapable of supporting the maximum transfer rate of its connected SCSI bus. In other words, a single Ultra160 SCSI hard drive will not tranfer data at 160 MB/second. Only by striping several drives together will the real potential of Ultra160 SCSI be appreciated.
Fibre Channel
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This page was last updated on 05/09/02.