Oracle RAC - Oracle為什麼不建議使用交叉線作為心跳線

Oracle不支援使用交叉線作為ClusterWare的內部連線， 這裡的Not Support不是說交叉線不能用，而是說Oracle不建議這樣做。

在Metalink上關於這方面的描述，摘錄一下：

CROSS OVER CABLES ARE NOT SUPPORTED.
The requirement is to use a switch:

Detailed Reasons:
1) cross-cabling limits the expansion of RAC to two nodes
2) cross-cabling is unstable:
a) Some NIC cards do not work properly with it. They are not able to negotiate the DTE/DCE clocking, and will thus not function.
These NICS were made cheaper by assuming that the switch was going to have the clock. Unfortunately there is no way to know which NICs do not have that clock.
b) Media sense behaviour on various OS's (most notably Windows) will bring a NIC down when a cable is disconnected.
Either of these issues can lead to cluster instability and lead to ORA-29740 errors (node evictions).

Due to the benefits and stability provided by a switch, and their afforability ($200 for a simple 16 port GigE switch), and the expense and time related to dealing with issues when one does not exist, this is the only supported configuration.

實際上，交換機的引入是為了更高的擴充套件性和穩定性，這是合理的投入，在搭建RAC環境時值得投入。