IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Organisation Remarks
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Enable Disk Read After Write Verify and is set to OFF in Netware 4.11. In
order to activate the function Hot Fix I, this parameter must be set to ON.
Hot Fix II, however, also functions in the default setting of Netware 4.11.
Hot Fix II has a similar fault tolerance to Hot Fix I, but only for mirrored
or duplexed disks. Unlike Hot Fix I, errors may even be corrected when the
data is read, as the information is redundant. If problems are detected when
the data is read, the sector of the disk is marked as faulty and a sector from
the Hot Fix area is used as a replacement. In this case, the intact
information from the mirrored or duplexed disk is read and the information
from the replacement disk for this area is automatically added to the faulty
sector.
As disks themselves are now highly intelligent and similar mechanisms are
available internally, Hot Fix I and II are of little importance today. If
sectors in the Hot Fix area are occupied despite modern disks, it is
necessary to change the disk immediately.
The Hot Fix area can be configured when a Netware partition is created.
Novell Netware suggests a size for the Hot Fix area which is adequate for
the size of the Netware partition. The relative size decreases as the size of
the partitions increase.
- Disk Mirroring (System Fault Tolerance II)
For disk mirroring two identical hard disks should be connected to the
same controller of a server. Nevertheless, it is also possible to mirror hard
disks which are not identical. The only requirement is that the data areas of
the two Netware partitions of the disks to be mirrored are the same size.
The data is stored simultaneously on both hard disks. If one disk fails, the
second disk will be used without a loss in availability.
- Disk Duplexing (System Fault Tolerance II)
Disk Duplexing means the installation of two hard disks and their
controllers. With this mechanism not only a hard disk failure can be
remedied, but also the failure of a hard disk controller can be recovered. In
disk duplexing, the power supply of the hard disks should also be
redundant, which is usually only possible with external disk systems.
- Server Mirroring (System Fault Tolerance III)
Server mirroring is the highest level of fault tolerance against hardware
failures. Two identical Novell Netware 4.x servers are employed
simultaneously and "in parallel" in the network. However, it must be kept
in mind that the secondary server is only available on standby and does not
take over the work in the network unless the primary server fails.
The servers are connected via their own high speed network. If one servers
fails, its tasks are carried out by the secondary server.
The decision whether measures other than Hot Fixes have to be employed
depends on the required availability of the network.
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IT-Baseline Protection Manual: Oktober 2000