Compaq AA-Q88CE-TE manual Standby for Shadows, Performance

Server Shadowing and Recovery

B.4 Shadow Site Failure and Journaling

B.4.1 Maximum Journal Size

The current maxima for the size of a journal are:

Number of blocks per disk: 524288

(This is max_segments_per_disk * disk_blocks_per_segment, or 16384 times 32.)

Number of disks per journal: 16.

B.5 Standby for Shadows

Shadowed sites can either be two nodes within a single cluster, or can be two separate clusters. In the second case it is also possible to configure standby servers on another node of each of these clusters, so that failure of a single node within one of the shadow sites does not stop the shadow site from functioning. Multiple concurrent copies of the server processes are allowed on each site.

This implies that up to four nodes can be configured to serve a particular key range. (see Figure B–1).

Figure B–1 Four Node Shadow/Standby Configuration

NODEA

Primary

Shadow

NODEP

Secondary

Shadow

NODEB

Primary

Standby

NODEQ

Secondary

Standby

Cluster C1

Cluster C2

B.6 Performance

The performance of a shadow pair compares with a transaction which spans two nodes, with the addition of one extra protocol message which is required to ensure that the transactions are presented in the equivalent order.

B–4Server Shadowing and Recovery