You may have been surprised when you first heard of backup strategies for ASM because ASM doesn't have any physical structure (no physical datafiles); it is just a special kind of instance, and there is actually no need to back it up. Having said so, it is strongly advised to back up all the important information in case of a disaster.
Pre-Oracle ASM 11g, there was no direct option to back up the ASM configuration and its metadata information. However, the recommended option in pre-11g was to gather the important information by spooling it in a text or HTML file through querying the ASM specific dynamic views, such as
V$ASM_DISK, V$ASM_FILES, V$ASM_DISKGROUP, V$ASM_CLIENT, and so on.
With 11g ...