efs2tar is a tool that converts SGI EFS-formatted filesystem images (ie, the result of dd-ing a whole device in to a file) in to tarballs. It was based entirely on NetBSD's sys/fs/efs (source).

$ go install github.com/sophaskins/efs2tar
$ efs2tar -in ~/my-sgi-disc.iso -out ~/my-sgi-disc.tar

The Internet Archive has several discs in its collections that are formatted with EFS.

• any type of file other than directories and normal files (which is to say, links in particular do not work)
• partition layouts other than what you'd expect to see on an SGI-produced CDROM
• any sort of error handling...at all
• that includes verifying magic numbers
• preserving the original file permissions
• I've only tested this on like, one CD