可以大于2T
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

在 Oracle 12c之前，ASM 单盘有一个 2T 的限制，当创建磁盘组单盘超过 2T 时，将会遇到诸如 ORA-15018, ORA-15099 的错误：

ORA-15018: diskgroup cannot be created

ORA-15099: disk ‘/dev/mapper/ORA_data1p1’ is larger than maximum size of 2097152 MBs

MOS 文档 1077784.1 明确说明了这个限制，在Oracle 10g 和 Oracle 11g中，这个问题都是硬限制。

那么到了Oracle 12c 中，这个限制已经被去除，单盘最大限制是 4PB 起。