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Before going into detail, some information on the so-called Hot Plug of fault tolerant disk
arrays (RAID 1/4/5/10) is given below.
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Fault tolerant means that a hard disk which is part of a RAID 1/4/5/10 Array Drive can fail
without causing data loss on the Array Drive. At the same time, the Array Drive remains fully
accessible. Obviously, the Array Drive then lacks the redundant data, therefore the defective
disk should be replaced by an intact one as soon as possible. In chapters C (
RAIDYNE
Quick-Setup
) and L (
GDTSETUP in Detail
), we have shown with various examples how to ex-
change a defective drive with GDTSETUP. Moreover, we described the functioning of the so-
called Hot Fix drive. This "constantly available spare part when needed" automatically inte-
grates itself into the Array Drive and is therefore the quickest means of regaining a redun-
dant Array Drive.
The Hot Plug function enables the replacement of a drive of an Array Drive (either in the
ready
or
fail
state) while the system continues to run, that is, without having to shut down
the NetWare fileserver for instance. A drive replacement may not only become necessary
when the drive has already failed, but also when there are signs that a failure could occur
soon (strong whistling of the hard disk, or constant retries of the read/write head).
Only those users with thorough knowledge of RAID and the ICP Controller should use the
Hot Plug function. Improper use can lead to data loss. (Naturally, we have integrated all
kinds of security provisions into the ICP Controller and GDTMON. But how can we prevent a
user from plugging out the wrong drive?). We recommend that you document each Array
Drive immediately after its configuration with GDTSETUP. This record should at least com-
prise the following information:
To which ICP Controller has the Array Drive been connected ?
Which SCSI devices (hard disks) are part of the Array Drive ?
To which SCSI ID have they been set ?
Which SCSI devices terminate a SCSI channel ?
In addition, the SCSI devices themselves should be labeled with the above information. The
following is an example of such a label.
&[\]W
&
: controller number
[
: SCSI channel
\
: SCSI-ID
]
: Logical Drive number
W
:
= terminated,
= not terminated
Example:
%
controller number 1, SCSI channel B, SCSI-ID 6, Logical Drive number 3, terminated. The
menu option
Save Information
of GDTSETUP, GDTMON program can be of help when setting
up the documentation.
How does the Hot Plug mechanism work ?
During the Hot Plug, the SCSI channel of the ICP Controller to which the drive to be ex-
changed is connected, is temporarily "halted" (for the time needed for the exchange), so
that the drive can be disconnected from the SCSI bus and replaced without any risk. After
the replacement, the SCSI channel halt is lifted and the firmware automatically begins to
