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Glossary
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Primary
system |
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The
initial computer system on which the application(s) and users will
be running. The Primary System is typically at least as powerful as
the Standby System .
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Standby
system |
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The system that maintains a mirrored, concurrent copy of the user's
application(s), data bases, and programs. This system is ready to
take over operation of the mirror Primary System if the Primary System
becomes untrustworthy. |
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Normal
mode |
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The time when the Primary System is fully operational; the users and
application(s) are running on the Primary System. |
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Fallback
mode |
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The time when the users and application(s) have been moved to the
Standby System . The only trustworthy copy of the data base and application(s)
are on the Standby System. |
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Mirroring
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The use of software and hardware to effect an unnoticed duplication
of data across multiple disk drives. A hot mirror means
that data is dynamically replicated across the disk drives; a cold
mirror means that the data is replicated on demand across
the disk drives. SavWareHA constructs a hot mirror. |
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I/O
link |
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SavWareHA depends on at least two connections between the primary
and Standby System s. One of these connections is the I/O link that
handles most, if not all, of the connectivity needs of a typical SavWareHA
system. This I/O link can be implemented as a 10BaseT, thin Ethernet,
RS422, or similar connection depending on the choice of serial device
for connectivity. |
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Serial
link |
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Serial ports on each of the systems can be connected together to form
a link between the mirrored systems. This serial link is used by the
monitor program on the Standby System as an additional way to check
the status of the Primary System . The serial link allows the monitor
program to distinguish between a network failure and a system failure.
No user data is transmitted via the serial link. |
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Data
link |
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SavWareHA's other connection between the primary and secondary system
is the path through which all data is transferred between the mirrored
filesystems. This link is usually a point-to-point link, implemented
typically with 100BaseT or 10BaseT Ethernet; for short distances,
10Base2 (coax) may also be used, with proper termination. A SCSI connection
may also be used.
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Regeneration
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The block by block duplication of one side of a mirror onto the other.
This creates an exact copy of the source side onto the destination.
All information is duplicated: ‘fdisk’ and ‘divvy ’
tables, as well as Unix filesystem information. |
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