It's not true. ASM does not convert files.
You can copy file from ASM to any filesystem, but the contents and format (big or little endian) of files will be the same.
You must use RMAN to Convert Datafiles, it change datafile contents and format.
Some Platforms has compatibility between them, on this case, you need just copy datafile and start database without conversion.
Migration Of An Oracle Database Across OS Platforms (Generic Platform) (Doc ID 733205.1)
Matrix compatibility of migrate datafiles to different platform without perform conversion:
Data Guard Support for Heterogeneous Primary and Physical Standbys in Same Data Guard Configuration (Doc ID 413484.1)
This is from 11.1 documentation regarding ASM CP command (dated 2007)
The format of copied files is portable between Little-Endian and Big-Endian systems if the files exist in an ASM disk group. ASM automatically converts the format when it writes the files. For copying a non-ASM files from or to an ASM disk group, you can copy the file to a different endian platform and then use one of the commonly used utilities to convert the file.
- 11.2 documentation says does not mention endian and says (this is dated 2012)
cpcommand performs a bit-wise copy. There is no data transformation.
However in oracle support there is this June 2013 bug report and fix (byte order is same as endian). We are at 18.104.22.168. Note that it says it was fixed in version 11.2.03 it appears it did not always work properly prior to this version
Are two different things.
ASM is a filesystem with own endian, which is platform dependent.
Datafile is a File which have also its own endian and is stored over ASM Disk (Filesystem) which have its own endian.
Datafile of my database on AIX have Big Endian stored on ASM Disk (Filesystem) with Big Endian.
But I can convert this Datafile to Little Endian on AIX (i.é RMAN Convert datafile on source before move to destination) and store the Datafile Little Endian over ASM Disk with Big Endian format.
So, in this case I can use ASM CP from Big ENDIAN to move datafile converted (Little endian) to my destination which is ASM with Little Endian.
How to Migrate to different Endian Platform Using Transportable Tablespaces With RMAN (Doc ID 371556.1)
If the source files are on ASM diskgroup and target platform has different endianess , the CONVERT command needs to be executed. The files cannot be copied directly between two ASM instances of different platform.