Why choose '/dev/oracleasm/disks/*' instead of 'ORCL:*' as diskString?

I'm having an issue installing Oracle Grid Infrastructure 11.2 on RHEL5 Virtual Box.

The final step creates the ASM Diskgroup, and failure with ORA-15020.

The error occurs if I specify the diskString path as any of:

/dev/oracleasm/disks

/dev/oracleasm/disks/*

But if I leave it alone, so that it defaults to 'ORCL:*' then process completes successfully.

Now, this is only for dev purposes to test a few things.

My question is, assuming both worked fine,  what difference does it make having the diskString as 'ORCL:*' or '/dev/oracleasm/disks/*'/