Oracle Database 11g 中的 ASM 限制

如果 COMPATIBLE.ASM 或者 COMPATIBLE.RDBMS 小于12.1:
最大单盘2T，整体空间20PB
如果 COMPATIBLE.ASM 或者 COMPATIBLE.RDBMS 大于12.1:
单盘最大4PB，整体可以320EB

ASM - Scalability and Limits (Doc ID 370921.1)
ORA-15196 WITH ASM DISKS LARGER THAN 2TB (Doc ID 736891.1)

ASM 强制实施下列限制：
存储系统中包含 63 个磁盘组
存储系统中包含 10,000 个 ASM 磁盘
每个 ASM 磁盘的最大存储空间为 4 PB
每个存储系统的最大存储空间为 40 EB
每个磁盘组包含 1 百万个文件
最大文件大小取决于所使用的磁盘组的冗余类型：外部冗余为 140 PB（该值当前大于可能的数据库文件大小），正常冗余为 42 PB，高冗余为 15 PB。

注：在 Oracle Database 10g 中，外部冗余的最大 ASM 文件大小为 35 TB。
–Variable size extents
	* grows automatically with file size
–Benefits
	* Increase ASM file size
	* Reduce memory utilization in SGA
–100% automatic
–
–Note: RDBMS limits file size to 128TB
	* 63 disk groups
	* 10,000 ASM disks
	* 4 petabyte per ASM disk
	* 40 exabyte of storage
	* 1 million files per disk group
	* Maximum file size:
	* External redundancy: 140 PB
	* Normal redundancy: 42 PB
	* High redundancy: 15 PB

Understood your concern,You can not add disk more than 2 TB as a asm disk.Please check with your os admin to break the 3 Tb disk in to 1.5 Tb and then use it as a ASM disk.Following are few points to consider,

ASM provides near unlimited capacity for future growth, but does have some storage limits.
For example, ASM has the following limits on the number of disk groups, disks, and files:
1.) 63 disk groups in a storage system
2.) 10,000 ASM disks in a storage system
3.) 1 million files for each disk group

Without any Oracle Exadata Storage, ASM has these storage limits:

1.) 2 terabytes (TB) maximum storage for each ASM disk
2.) 20 petabytes (PB) maximum for the storage system
With all Oracle Exadata Storage, ASM has these storage limits:
3.) 4 PB maximum storage for each ASM disk
4.) 40 exabytes (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 63 disk groups. This is a limitation on the number of ASM disks, not necessarily the number of spindles. A storage array could group multiple spindles into a LUN that is used as a single ASM disk. However ASM is currently limited to 2 TB in a single disk unless using Oracle Exadata storage.

File size limits are dependent on the value of the disk group compatibility attributes. ASM supports file sizes greater than 128 TB in any redundancy mode when the COMPATIBLE.RDBMS disk group attribute is set greater than10.1. 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, ASM file size limits are:

1.) External redundancy: 16 TB
2.) Normal redundancy: 5.8 TB
3.) High redundancy: 3.9 TB