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rebuild the new drive. The halting and the halt-lifting of the GDT SCSI channel is controlled
by the Hot Plug function. The above mentioned halting of the SCSI channel avoids that in-
terferences caused by plugging off the drive impair the functioning of other drives still ac-
tive on this SCSI channel. Moreover it prevents the possible destruction of the SCSI
processors of the ICP Controller or the SCSI protocol ICs of the SCSI drives. However, this
implies that none of the SCSI devices of the halted SCSI channel can be accessed during
the time the defective drive is being exchanged. This may affect, for example, other drives of
this Array Drive, other Array Drives, simple Host Drives (of the type disk etc.), and
Not Direct
Access Devices
(CD-ROMs, DAT streamers, MOs, etc.). If the ICP Controller has only one SCSI
channel, or if all SCSI devices are connected to one single SCSI channel, then no SCSI de-
vice can be accessed during the time of replacement. Therefore, it is evident that it is best if
the ICP Controller had as many SCSI channels as possible and that all SCSI devices were
distributed equally to the available channels in order to avoid that the Array Drive or other
SCSI devices cannot be accessed during the Hot Plug drive replacement. This non-
accessibility of the Array Drive during the replacement is communicated to the operating
system by the GDT driver program that integrated the ICP Controller into the operating sys-
tem. If the period of non-accessibility becomes too long a system error may occur. The Hot
Plug should be carried out as quick as possible.
Various manufacturers offer so-called
Disk Shuttle
(sometimes also called
Disk Shelf
) subsys-
tems. There are two categories of these subsystems: Non-Intelligent and Intelligent. Both
generally consist of the shuttle itself, a shock safe metal or plastic enclosure containing the
hard disk, a frame which is mounted in the computer case or in an external subsystem, and
a sufficient cooling system.
Especially the last component is very important. If the hard disks run too hot, it is very likely
that they will fail. In addition, their lifetime is reduced dramatically. The mounting frame
has appropriate slide rails and locks that fit with the shuttle. The shuttle can be slid into or
out of the mounting. When using any of these systems you have to make sure that the SCSI
termination (regardless of whether the drive has been terminated or not) is made in the
mounting frame. In addition, always use high quality connectors for the SCSI buses and the
power supply. It is very important that during the plug out, the SCSI bus is disconnected
first, and then the power supply. When plugging in again, the order is vice versa.
The Non-Intelligent subsystems have no communication with the ICP Controller and no in-
telligent backplane (i.e., with sensors).
If it is intended to avoid this halting and halt-lifting of the GDT SCSI channel, an Intelligent
subsystem is needed. The ICP Controllers support two different types of such subsystems:
SAF-TE and DEC
(TM)
fault bus compliant subsystems. SAF-TE stands for SCSI Accessed Fault-
Tolerant Enclosure and is soon becoming part of the SCSI specification. The DEC
(TM)
fault
bus is a special technology from Digital Equipment
(TM)
.
With these subsystems, the ICP Controller enables the performance of the so-called
Auto
Hot Plug
, which reduces the whole Hot Plug procedure to the simple replacement of the disk
shuttle which contains the desired hard disk. Furthermore, these subsystems have typically
several LEDs to indicate for example the disk shuttle which contains the defective hard disk.
..
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This option displays details on the ICP Controller. For example, how much Cache RAM the
ICP Controller has and what the current termination setting of the various SCSI channels is.
