UnitControl 2.5 (29.04.1996) ============================== The Workbench tool UnitControl allows you to carry out device specific settings for each individual device connected to the SCSI bus. It also allows you to control removable media and tape streamers. Start UnitControl by double-clicking on the icon. The following main window appears: The upper part of the window displays the units present on the SCSI bus. You can select these for further actions by clicking on the units. The title of the selected unit then changes color. If you should have more units than will fit in the window then you can scroll through the list with the scroll bar on the right-hand side of the display window. --- Quit As long as none of the devices is selected, only the Quit button will be available from the five buttons in the lower part of the main window. By clicking on this button you will exit UnitControl. As soon as you select a device the other buttons become available. These buttons allow you to control various actions of the connected device. --- Eject: If the SCSI device supports software controlled ejection of the medium, then this button will eject the medium. For devices which do not support ejection of mediums the activation of this button normally causes the drive motor to stop. --- Stop: This button turns off the drive motor of the device selected. Hard disks or removable drives which you only use sporadically can be turned off in this way to avoid unnecessary wear and tear and power consumption. --- Start: A device deactivated with Stop or for other reasons can be reactivated by using this button. --- Rescan Rescan SCSI Bus for new SCSI units. --- Mount Try to mount partitions from a unit. --- Prefs Allows to set a Resident Tag with 'Save'. May speedup your next reboot. --- x x x x x x x x Unit Scan Array The unit which is activated here is scanned during the boot phase. --- SCSI Reset Delay The seconds the device waits after a SCSI Reset. --- Inquiry Error Delay The seconds the device waits after an Inquiry Error --- Inquiry Error Retry The retry count for an Inquiry after an Error. --- Error Retrys The retry count for an SCSI Operation after an SCSI Error. --- Selection Timeout The count of chip ticks the chip uses to determine that a selection failed. --- Lun Reselection Using Reselection between single Luns of a Unit. I know no Unit which supports this. --- Options: By activating this button a new window is opened, where you can set special device parameters for the unit selected. This tool can be very useful if problems occur in transmitting data to a certain device without other units being affected. The settings under Special also allow the data transmission to be adjusted to maximum speed. You should have various information about the selected device at hand so that you can set the options correctly. In general, you can find the information in the datasheets or the operating instructions of the connected device. --- Asynchron/Synchron This button switches between synchronous and asynchronous access to the device. The default setting is determined from the information contained in the RDB. In synchronous mode a certain number of data words are transferred in a block, followed by a handshake. This mode allows higher transmission rates if the device supports them. Unfortunately the likelihood of errors in the transmission also increases, in proportion to the size of the block to be transmitted. In synchronous mode up to 10 MByte data transmission rate is possible. The maximum transmission rate for a particular device is, however, affected by both the device itself and the length and type of the SCSI cable used. When you activate the synchronous mode, the SCSI Controller and the device concerned automatically negotiate the maximum transmission rate. This is mostly 10 Mb/sec for FAST SCSI devices, and 4 or 5 Mb/sec for normal SCSI or SCSI-II devices. If 10 Mb/sec is automatically set this does not mean that the transmission can take place securely at this rate when the synchronous mode is activated. If occasional transmission errors occur or the hard disk "hangs up" at high transmission rates after setting the synchronous operation mode, this can be an indication that the connection to the device is not secure enough for the chosen speed. This problem occurs because the transmission rates are extremely dependant on the cable length. In such a case you should set the rate lower to prevent transmission faults. Experiments have shown that the highest setting for the synchronous data transmission is not necessarily the fastest. Today, nearly all manufacturers rate the speed of their hard disks at 10 Mb/sec, which relates to the SCSI bus speed. In reality, today (Autumn 1993) hardly any hard disks transfer more than 4 Mb/secec as usable sustained output. In practice, with a fast drive in the gigabyte range, for example, it has been shown that the transfer values determined from the common test program DiskSpeed 4.2 were faster in synchron-6MB-mode than in synchron-10MB-mode. It is therefore sensible to try out various settings with the help of a test program when determining the optimal setting for a certain drive. --- Slider BYTES/HANDSHAKE This adjuster allows you to set the number of bytes to be transmitted per handshake. The optimal value for this setting can only be determined through trial and errors. A setting which is too high can cause transmission errors, which significantly lowers the speed or even causes read errors. The regulator is set to 8 as a starting point, which will provide you with an acceptable transmission rate with an extremely low likelihood of errors. --- Slider SYNCHRON MB/S Here you can manipulate the speed of the data transmission in synchronous operation. As previously explained, the SCSI Controller and the device concerned negotiate the maximum transmission rate. If you should have problems with the device connected, in the form of read errors or SCSI bus hang-ups despite this, then you can decrease this value to check whether the device or the connection (cable) are unable to correctly execute the high transmission speed. This problem can also occur if the device accepts 10 Mb/sec as a permitted value because the transmission rate is extremely dependant on the cable length. Both the Bytes/Handshake and the Synchron Mb/sec adjusters should always be considered as linked. To find the real best possible setting some test and trial work is necessary. In general, the default values should provide secure transmission at the optimum transmission rate. --- Reselection SCSI devices are able to hand over the bus during long continual operations to allow other devices to transmit data. At the end of the operation the device then demands the bus once again to convey its own results. This process is called Reselection. As not all devices support this process and some devices which do support it do not work correctly in this mode, it is possible to activate or deactivate this mode specifically for each device. Reselection has practically no effect in access to an individual device. Reselection requires additional protocol so you should expect a slight loss of performance. Only when several devices are active simultaneously on the bus is an increase in performance likely. --- FWC Mode Use this to enable/diable the write RAM cache. --- Removable Selects if a SCSI unit is a removable or not. --- Quit Quit allows you to exit the Special window, but it does not change anything in the device configuration. --- Set Set allows you to save the settings made for the device. --- Reset This resets the SCSI bus. If the SCSI bus should hang up (which you will recognise because the bus activity LED on one or more of the drives connected will be lit continuously) then you can return the bus to an active state with this button. Reset affects the whole bus, not only the device selected. If other devices are transmitting data when this button is activated, it will be lost. This can vary from harmless read errors to the loss of whole partitions. Use reset only if there is no disk activity in the system or as the very last resort if the SCSI bus has crashed .
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