A few weeks ago many thought a breakup up the eurozone was "unthinkable". Today, "disaster plans" are being made by numerous banks to allow for just that event.

The Wall Street Journal reports Banks Ponder Euro-Zone Split

A key part of the world's foreign-exchange trading infrastructure is bracing itself for the possibility of a breakup of the euro zone, the latest sign investor concerns about the Continent's debt crisis are on the rise.

CLS Bank International, which operates a platform in which banks settle most of their currency trades, is running "stress tests" to prepare for the possible dissolution of the euro, according to people familiar with the situation.

Some of the 63 banks that co-own CLS are making similar plans. "We always plan for contingencies," said a senior executive at one of the largest currency-dealing banks.

New York-based CLS is by far the biggest name in the currency market known to be making preparations for such a scenario. Analysts with Japanese bank Nomura Holdings said Friday that a euro breakup is a "very real risk," while HSBC Holdings analysts told clients on Tuesday that it's "not unimaginable" for countries to leave the euro zone.

This is the kind of discussion and action that is needed because a breakup appears inevitable.