Home > Workload Solutions > Oracle > White Papers > Oracle ASM on ScaleIO Best Practices > ASM extents
ASM organizes data within diskgroups into extents.
An ASM extent is distinct from an Oracle table extent. An ASM extent consists of one or more allocation units.
It is important to remember that when using ASM mirroring, ASM mirrors by ASM extent, not disk or diskgroup. Although Dell EMC discourages the use of ASM mirroring, for those DBAs who wish to leverage the feature it must be remembered that this extent based mirroring when used in conjunction with MESH mirroring means that ASM has no visibility to the physical disk layout, and therefore ASM mirrored extents may be allocated back to the same physical device undermining the protection of the mirror.
In ASM 11g, the extent size increases with the size of the ASM file as shown in Table 7.
Table 7. ASM file extents
Extents in ASM File |
Extent Size (11.1) |
Extent Size (11.2) |
0 to 19,999 |
1 * AU Size |
1 * AU Size |
20,000 to 39,999 |
8 * AU Size |
4 * AU Size |
40,000 and higher |
64 * AU Size |
16 * AU Size |
Note: The DBA has no direct control over the extent size in ASM.