Putting the database in backup mode before making file system changes We are planning to make a small change in the Linux file system. To be on the safe side, I thought I would take a SAN-level snapshot of all the drives beforehand. I was thinking I should put the Oracle database in backup mode:

Alter system archive log current;
Alter database begin backup;
-- after the SAN snapshot finish--
Alter database end backup;
Alter system archive log current;


Someone said this command is deprecated from 9i.

My question is, if I go ahead and use this, will it be ok? Or is there another way to do this?

Note: I don't want to use RMAN's full backup as this will take 6 hours.
The method you describe is ok. This method was the backup method used before Oracle introduced RMAN and is still valid. It is still used by tools that do snapshot backups (like Netapp's backup tool for Oracle) and I often use this in similar situations.
You also should make a controlfile backup if all the controlfiles are on these disks.