Introduction

The documented AWS EC2 EBS volume attachment limit is 27. The attachment limit affects the maximum number of Oracle ASM disks.

EC2 volume limit

Amazon AWS documents a 27-volume attachment limit. I have found that a t2 type creation attempt with 28 EBS volumes will abort.

Attempting to create an m5 (Nitro)  with 28 or more volumes will hang.

The attachment limit is 28, including network interfaces, volumes, and instance store volumes. EC2 instances with one network interface can have up to 27 volumes attached.

EC2 instances with more than 27 volumes

I am aware of t2 EC2 systems with as many as 44 volumes attached. I have no information about how this was done, and what the customer’s support expectations are. I would be concerned about how such a system would respond to a change of instance type.

Oracle Database

In planning an Oracle database installation, you may need file system mounts as well. /u01, for example. The underlying volume counts against the maximum attachment count.

In laying out an ASM setup, consider a simple design, with as few ASM disks and ASM disk groups as needed.

Conclusion

Based on the available public information, I recommend limiting the number of EBS volume attachments to 27. Oracle database administrators might want to simplify their ASM implementation.