I made the assembly of an ext4 volume. But it does not open on Windows server 2012. What procedure should I do to open it?
I believe you meant mounted a linux recovery point at the core server.
Windows is not capable to natively mount (recognize) linux file systems. So even if you were successful mounting it, the OS would not be able to parse through the ext4 file system and show you contents.
Please review this KB article for the proper procedure (using a linux machine to mount the recovery point).
Additionally, there are 3rd party utilities that can allow you to mount and view linux file system volumes on Windows, such as "ext2fs" and others. We do not support them, but they do allow you to see certain Linux file systems in a Windows OS. This all depends what your end goal is with the mount procedure.
You can try to format the ext4 to NTFS,which is compatible with Windows Server 2012. Ext3 or third extended file system is a file system used by the linux kernel. This is a default file system in linux for many applications and popular linux distributions. If the windows cannot complete the format, you can turn to AOMEI Partition Assistant, a professional formatting tool.