25.2.4 System configuration examples of standby-less system switchover (effects distributed)

Organization of this subsection
(1) System configuration example
(2) Determining the switching destination for each server
(3) Configuration with five units

(1) System configuration example

Figure 25-25 shows a system configuration example of standby-less system switchover (effects distributed). When an error occurs in the regular unit, processing intended for the back-end servers in the primary system where the error occurred is divided in units of back-end servers, assumed by multiple running server machines, and executed.

Figure 25-25 System configuration example of standby-less system switchover (effects distributed)

[Figure]

Explanation
  1. When an error occurs in Unit 1, BES1 executes its processing in Unit 2 as a guest BES, and BES2 executes its processing in Unit 3 as a guest BES.
  2. If an error occurs in Unit 2 while Unit 1 is still in error status, BES1, BES2, BES3, and BES4 all execute their processing in Unit 3 as guest BESs.

(2) Determining the switching destination for each server

When you use the standby-less system switchover (effects distributed) facility, HiRDB takes the following issues into consideration in determining the switching destinations for the individual servers:

When standby-less system switchover (effects distributed) is used, HiRDB uses the following procedure to determine switching destinations:

Procedure
  1. Determines the switching-destination unit for the server that has the highest priority among all servers. The following are the determination criteria:
    [Figure]Balancing the number of servers to be switched from one unit to other units
    [Figure]Balancing among the units at the switching destination the number of servers that will share a global buffer
  2. From i = 1 to [number-of-units-in-HA-group - 2], steps 3 through 9 are repeated.
  3. Selects a server with priority ranking of i + 1 whose switching destination has not been determined.
  4. If there is an applicable server, the process proceeds to step 5. If there is no applicable server, i = i + 1 is set and the process returns to step 3.
  5. Assumes that switching destinations 1 through i must be determined for the selected servers, and that the unit to which these servers belong is the erroneous unit.
  6. Units other than the erroneous unit are selected as switching destination candidates.
  7. From the servers belonging to the erroneous unit, all servers that have switching destination candidates as defined switching destinations are extracted, and it is assumed that guest BESs for the server in question are allocated to the switching-destination unit with the highest priority.
  8. From the servers belonging to the erroneous unit, all servers that do not have switching destination candidates as defined switching destinations are extracted, and the i +1-th switching-destination unit is determined for each server. The following are the determination criteria:
    [Figure]The unit with the smallest number of guest BESs is selected.
    [Figure]Units in which fewer guest BESs share a global buffer with the server are selected.
  9. Returns to step 3.
(a) Configuration with four units

The standby-less system switchover (effects distributed) facility is applied to the following configuration consisting of four units:

[Figure]

In this case, a global buffer is shared in each of the following groups:

  1. Determining the switching-destination unit with the highest priority
    An example is shown that determines the switching-destination unit with the highest priority for BES3B. A switching destination is determined so that it does not coincide with servers that share the same global buffer (BES1B and BES2B) or BES3A. Specifically, unt1 is selected because the switching destination of BES1B (unt3), the switching destination of BES2B (unt4), and the switching destination of BES3A (unt4) cannot be selected.
    ServerHost BESHighest prioritySecond priorityThird priority
    BES1Aunt1unt2AllocatedAllocated
    BES1Bunt3AllocatedAllocated
    BES1Cunt4AllocatedAllocated
    BES2Aunt2unt3AllocatedAllocated
    BES2Bunt4AllocatedAllocated
    BES2Cunt1AllocatedAllocated
    BES3Aunt3unt4AllocatedAllocated
    BES3Bunt1AllocatedAllocated
    BES3CAllocatedAllocatedAllocated
    BES4Aunt4AllocatedAllocatedAllocated
    BES4BAllocatedAllocatedAllocated
    BES4CAllocatedAllocatedAllocated
  2. Determining the switching-destination unit with the second or subsequent priority
    An example is shown that determines the switching-destination unit with the second priority for BES2B.
    First, unt4, which is a defined switching destination of BES2B, and unt2, to which BES2C belongs, are assumed to be erroneous units (step 5), and unt1 and unt3 are selected as switching-destination candidates (step 6). Next, from the servers belonging to the erroneous units (unt2 and unt4), servers (BES2A, BES2C, BES4A, and BES4C) that have the switching destination candidates as defined switching destinations are extracted, and it is assumed that guest servers are allocated as shown below (step 7).
    BES2A: unt3; BES2C: unt1; BES4A: unt1; and BES4C: unt3
    Next, servers (BES2B and BES4B) that do not contain the switching destination candidates as defined switching destinations are extracted, and the switching-destination unit with the second priority is determined. In this case, the number of guest BESs is the same for unt1 and unt3, and BES2B and BES4B share a global buffer, and therefore, BES2B is switched to unt1 and BES4B is switched to unt3.
    ServerHost BESHighest prioritySecond priorityThird priority
    BES1Aunt1
    Switching-destination candidate unit
    unt2unt4Allocated
    BES1Bunt3unt2Allocated
    BES1Cunt4unt2Allocated
    BES2Aunt2
    Erroneous unit
    unt3unt1Allocated
    BES2Bunt4unt1Allocated
    BES2Cunt1AllocatedAllocated
    BES3Aunt3
    Switching-destination candidate unit
    unt4AllocatedAllocated
    BES3Bunt1AllocatedAllocated
    BES3Cunt2AllocatedAllocated
    BES4Aunt4
    Erroneous unit
    unt1AllocatedAllocated
    BES4Bunt2AllocatedAllocated
    BES4Cunt3AllocatedAllocated

Table 25-11 shows an example of switching destination definition in a 4-unit configuration.

Table 25-11 Switching destination definition example in a 4-unit configuration

ServerHost BESHighest prioritySecond priorityThird priority
BES1Aunt1unt2unt4unt3
BES1Bunt3unt2unt4
BES1Cunt4unt2unt3
BES2Aunt2unt3unt1unt4
BES2Bunt4unt1unt3
BES2Cunt1unt3unt4
BES3Aunt3unt4unt2unt1
BES3Bunt1unt4unt2
BES3Cunt2unt4unt1
BES4Aunt4unt1unt3unt2
BES4Bunt2unt3unt1
BES4Cunt3unt1unt2

(3) Configuration with five units

The standby-less system switchover (effects distributed) facility is applied to the following configuration consisting of five units:

[Figure]

In this case, a global buffer is shared in each of the following groups:

Table 25-12 shows an example of switching destination definition in a 5-unit configuration.

Table 25-12 Switching destination definition example in a 5-unit configuration

ServerHost BESHighest prioritySecond priorityThird priorityFourth priority
BES1Aunt1unt2unt5unt3unt4
BES1Bunt3unt4unt2unt5
BES1Cunt4unt3unt5unt2
BES1Dunt5unt2unt4unt3
BES2Aunt2unt3unt1unt4unt5
BES2Bunt4unt5unt1unt3
BES2Cunt5unt4unt3unt1
BES2Dunt1unt3unt5unt4
BES3Aunt3unt4unt2unt1unt5
BES3Bunt5unt1unt2unt4
BES3Cunt1unt5unt4unt2
BES3Dunt2unt4unt5unt1
BES4Aunt4unt5unt3unt1unt2
BES4Bunt1unt2unt3unt5
BES4Cunt2unt1unt5unt3
BES4Dunt3unt5unt2unt1
BES5Aunt5unt1unt4unt2unt3
BES5Bunt2unt3unt1unt4
BES5Cunt3unt2unt4unt1
BES5Dunt4unt1unt3unt2