Nanofunk reported on a possible modification of the Promise Pegasus Thunderbolt RAID to host 6x3TB Hard Drives for a total of 18TB storage back in July 2011. While we did not have any issues with Hitachi Deskstar 3 0F12450 and Western Digital 3 TB SATA II Intellipower 64 MB Drives, other people repeatedly reported issues and even failures when the drives hold more than 11TB of data.
Currently, with the announcement of the Hitachi Deskstar 7K4000 4000GB, SATA 6Gb/s (0F14681) and the 4TB Deskstar 5K4000 as well as the 4TB Seagate Barracuda XT 7200RPM a total of 24TB could be reached when modding the Promise Pegasus just replacing the 2TB drives it comes with.
Tomshardware even reported on 5TB HDDs arriving in January 2012, so a modification to fit 30TB into the Promise Pegasus would be possible theoretically.
While all the drives are not available at the current time of writing of this article, please do consult the Promise Support if you are planning to do modifications or already did! Judging from the current feedback on modifications, updating the Promise Pegasus before an official answer or statement from Promise Technology is NOT RECOMMENDED!
Please send emails to Promise directly and ask them to react on the current limitations. I already did so – still waiting for response.