ASM provides striping by dividing files into equal-sized extents. Fine-grained striping extents are 128KB in size. For Oracle 10g, coarse-grained striping extents are 1MB in size. For Oracle 11g, coarse-grained striping extents can be 1, 2, 4, 8, 16, 32, or 64MB in size. Striping spreads each file extent evenly across all disks in the assigned disk group.
ASM also provides automatic mirroring of ASM files and allows the mirroring level to be specified by group. This mirroring occurs at the extent level. If a disk group is mirrored, each extent has one or more mirrored copies, and mirrored copies are always kept on different disks in the disk group.
There are three ASM mirroring options:
Two-way mirroring – Each extent has one mirrored copy in this option.
Three-way mirroring – Each extent has two mirrored copies in this option.
Unprotected mirroring – ASM provides no mirroring in this option, which is used when mirroring is provided by the disk subsystem.
