Oracle Automatic Storage Management(ASM) was introduced in release 10g. ASM is Oracle’s logical volume manager, it uses OMF (Oracle Managed Files) to name and locate the database files. It can use raw disks, filesystems, or files which can be made to look like disks as long as the device is raw.
ASM uses its own database instance to manage the disks. It has its own processes and pfile or spfile and uses ASM disk groups to manage disks as one logical unit. In some ways ASM makes things more complicated – like accessing the files, copying to different locations, and viewing the time stamps of the files. It’s considered good practice to create one disk group for data (DATA) and one for archive logs and fast recovery area(FRA) per ASM instance. One disk group gets created during the cluster install and configuration (OCR). For a larger production database it’s common for it to have its own DATA and FRA disk groups.