loss of data using a SAN

Hi, we are testing failovers for two Windows 2008 servers using an Oracle 11g R2 database on a SAN. The SAN is disabled/enabled between these 2 servers.

In the documentation it says:

Loss of data if the SAN drive is being written to when the HBA card is disabled. You must ensure that all interfaces are shutdown before implementing the failover process.

Question: How can you lose data on the SAN? Surely the SAN is just a set of disks and Oracle can recover using the redo logs once you enabled the SAN onto the secondary server?

Thank you.
Regards, Sheryl

and what if the write didn't happen to the disks, what then

Hi, thanks for the comment, but I don't understand. The database should only know about commits, which are written to the redo logs, if there is no commit then it would surely rollback the transaction.

Is using the SAN as a failover option not a good decision? Thanks.