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aware of the fact that this disk array does not have any redundancy until the defective hard

disk has been substituted. This means that if another hard disk should fail while the disk

array is without redundancy, all data is irretrievably lost. RAIDYNE offers two possibilities

of replacing a failed drive of an array for which no Hot Fix drive has been designated:

1. Replacement with GDTSETUP (we have just demonstrated this method)

2. Replacement by using the

Hot Plug function of GDTMON

The Hot Plug method allows you to replace a defective drive while the disk array continues

to work and without having to load GDTSETUP. When this method is used, the GDT SCSI

bus to which the defective drive is connected, is temporarily halted (that is, for the time

necessary for replacement), thus enabling you to disconnect the defective drive from the

SCSI bus without any risk. After the replacement, the SCSI channel halt is lifted again and

RAIDYNE automatically begins to rebuild the new drive. The halting and release of the GDT

SCSI channel is controlled by GDTMON, which is available for most operating systems

supported by the ICP Controller. The above mentioned halt of the SCSI bus serves to avoid

that interferences (spikes and glitches) which inevitably occur on the SCSI bus when the

defective drive is disconnected, impair the functioning of still intact drives on this SCSI

channel. 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. If all drives forming

the disk array are connected to one single SCSI channel the entire disk array cannot be ac-

cessed during the time of replacement. Therefore, it is evident that the ICP Controller

should have as many SCSI channels as possible and that all SCSI devices should be dis-

tributed equally to the available channels in order to avoid that the disk array or other SCSI

devices cannot be accessed during the Hot Plug drive replacement. The Hot Plug should be

carried out as quickly as possible.

The ICP Controllers also support the Intelligent Fault Bus (DEC ™ fault bus) and SAF-TE.

Both industry standards allow for a replacement without any program interaction. Simply

unplug the defective drive and plug in a new one. To make use of this very comfortable

methods, an intelligent subsystem (supporting either the Intelligent Fault Bus, or SAF-TE)

is required.

We would like to stress that the Hot Fix method is by far the most secure method

replacing a defective drive while the disk array is operational (see next example). First of

all, because it is completely automatic, and secondly because it does not imply any me-

chanical or electrical interventions on the disk array as the Hot Plug method does.

We shall explain GDTMON and the Hot Plug method more thoroughly later in this manual.

&([DPSOH5$,''LVN$UUD\V:LWKD+RW)L['ULYH

This example is applicable to ICP Controllers with the RAIDYNE firmware. What we call

Hot

Fix

drives is referred to as

Host Spare

drives in some literature. Most part of the installa-

tion is carried out as in our third example, so we do not repeat the explanation.

Do Step 1, Step 2 and Step 3 as described in example no. 3.

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We now leave level 2 (by pressing the <ESC>-key) and are back in the main menu. Now,

with the cursor keys n and p select Configure Array Drives and go to level 3 by pressing

<ENTER>.

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