在 Oracle 12c之前，ASM磁盘组中单块磁盘大小不能超过 2T，当创建磁盘组单盘大小超过2T时就报错。
ORACLE建议打补丁，但是即使应用补丁后，2TB仍然是个硬邦邦的限制
If the disk size is greater than 2TB, please resize the LUN/disk to a size under 2 Terabytes. Then you will be able to create the diskgroup.
It's ok to use disks with exactly 2TB size.
Note: Even with fix of 6453944 , 2TB is still the limit on 11.2 version on nonExadata set up
到了Oracle 12c 中，这个限制已经被解除，单盘最大限制为最起码4PB，文档有介绍这个改变>>>>>>>>Oracle ASM Storage Limits
Oracle ASM provides near unlimited capacity for future growth, but does have some storage limits.
Oracle ASM has the following limits on the number of disk groups, disks, and files:
511 disk groups in a storage system for Oracle Database 12c Release 1 or later
10,000 Oracle ASM disks in a disk group
65530 Oracle ASM disks in a storage system
1 million files for each disk group
Without any Oracle Exadata Storage, Oracle ASM has the following storage limits if the COMPATIBLE.ASM or COMPATIBLE.RDBMS disk group attribute is set to less than 12.1:
2 terabytes (TB) maximum storage for each Oracle ASM disk
20 petabytes (PB) maximum for the storage system
Without any Oracle Exadata Storage, Oracle ASM has the following storage limits if the COMPATIBLE.ASM and COMPATIBLE.RDBMS disk group attributes are set to 12.1 or greater:
4 PB maximum storage for each Oracle ASM disk with the allocation unit (AU) size equal to 1 MB
8 PB maximum storage for each Oracle ASM disk with the AU size equal to 2 MB
16 PB maximum storage for each Oracle ASM disk with the AU size equal to 4 MB
32 PB maximum storage for each Oracle ASM disk with the AU size equal to 8 MB
320 exabytes (EB) maximum for the storage system
With all Oracle Exadata Storage, Oracle ASM has the following storage limits:
4 PB maximum storage for each Oracle ASM disk with the AU size equal to 1 MB
8 PB maximum storage for each Oracle ASM disk with the AU size equal to 2 MB
16 PB maximum storage for each Oracle ASM disk with the AU size equal to 4 MB
32 PB maximum storage for each Oracle ASM disk with the AU size equal to 8 MB
320 EB maximum for the storage system
The maximum size limit of a disk group equals the maximum disk size multiplied by the maximum number of disks in a disk group (10,000).
The maximum number of disks across all disk groups is 10,000. The 10,000 disks can be in one disk group or distributed across a maximum of 511 disk groups. This is a limitation on the number of Oracle ASM disks, not necessarily the number of spindles. A storage array could group multiple spindles into a LUN that is used as a single Oracle ASM disk.
File size limits are dependent on the value of the disk group compatibility attributes. Oracle ASM supports file sizes greater than 128 TB in any redundancy mode when the COMPATIBLE.RDBMS disk group attribute is set greater than 10.1.
If COMPATIBLE.RDBMS is set to 10.1, the file size limits are less. For example, with COMPATIBLE.RDBMS equal to 10.1 and the AU size equal to 1 MB, Oracle ASM file size limits are:
External redundancy: 16 TB
Normal redundancy: 5.8 TB
High redundancy: 3.9 TB
