Apple’s new Mac Pro is the supercar of desktop computers, but it’s also trying to be a modular, upgradable workstation, and it’s not yet clear how Apple has balanced those two things. But we do have our first indication that the Mac Pro’s fancy new MPX Modules may not be a totally proprietary solution, in the form of two upcoming storage modules from Promise Technology that will be sold in Apple stores.

Promise, known for its Pegasus external RAID arrays and rack mount hard drive solutions, says it worked with Apple to announce versions that you can insert directly into the PCIe slots in the new Mac Pro. The product page says the new Pegasus R4i in particular counts as a bona fide MPX Module, one that adds up to 32TB of storage in a prebuilt RAID 5 array, meaning your data can survive in case one of its four hard drives happens to fail. (Presumably, the redundancy of RAID 5 means we’re talking about 24TB of actual usable storage, since it comes with four 8TB, 7200RPM magnetic drives.)

Since Promise apparently worked with Apple, it’s still not quite clear whether the new MPX Modules (which use both traditional PCIe and a second “all-new” PCIe connector that provides more power and data over a special Thunderbolt 3 backbone that Apple built into the new Mac Pro) are something just anyone can build for, or if you need approval and support, and possibly need to pay Apple some licensing fees like you do if you’re building for the Lightning connector on an iPhone.

Apple hasn’t yet replied to our request for comment about how the MPX Module idea will work more broadly.

We also don’t have pricing and availability on the R4i or its J2i counterpart yet, which fits up to two drives instead of four. But seeing how they’re listed on Apple’s official Mac Pro spec page now, it seems likely you’ll be able to buy them when you configure a Mac Pro this fall.