Promise Pegasus MPX module is a no-go for me not from heat dissipation point of view. It is the RAID 5 they use that is dangerous. (you should use either RAID6 or RAID5 with additional copy somewhere else) In fact if you Google it you can find almost every IT professionals against of using RAID5 on mechanical drive. The mass amount of reconstruction work will make a second drive failure more than an unlikely event. It is safer only for SSD assuming read failure are not likely.
IMO you should not try to mount large drives in a machine that is designed for maximizing performance. Making your editing from a SSD or NVMe volume. Once it's done move the archive to an external drive connected to Mac Pro either by Thunderbolt or 10Gb ethernet NAS. This type of mounting cage makes absolutely no sense for Mac Pro.
Most of what you’re saying is spot on, but it’s not relevant to the use cases for 2-3 internal HDDs in the MacPro. Not every drive is for back up, and not every end user is worried about rebuilding a RAID if a drive fails. The point is to be able to recover the data if the drive fails.
The reconstruction work necessary is moot given that you can reconstruct and pull your data off. At that point, the cost of buying new drives for the entire array is small. Also, if a user builds an array with 3-5 drives and 2 fail back to back then it’s a problem with the drives, not the RAID or the enclosure. Certainly a bad batch.
SSDs will always be safer, but most end-users looking to build an array are balancing speed, size, and cost. If they have $4000 to spend on a large, SSD array then perfect, but some need more than 12-16TBs, and mechanical is the best way to go.
Editing from SSD or NVMe poses the same problems. Speed, size, cost, etc. are all considerations in post production. If my project is 13TBs the array to store the files will cost me more with SSDs over mechanical for a not too much faster increase in speed.
Now as for the cage, again, every upgrade is going to be based on end user needs. Not everyone has the money for an SSD raid array and not everyone needs the fastest drives available. ProTools users have TBs of loops and data to store and don’t need SSDs to access it.
Freelance editors (using ProTools as well) who have libraries of templates, loops, filters, music, etc. also have to store their files close, don’t need them to be on an SSD, and don’t need them clogging up their system drive.
Some editors prefer to have internal scratch either as JBOD or in some form of RAID.
Others like myself like to backup the workstation on internal disks, as well as remote. So having 36TBs inside of the machine, (i.e. not needing an external enclosure, power, cabling) of regular hard disks isn’t a bad idea.
(Contrary to your "no one is buying them" statistic, an Apple business rep whom I contacted two months ago said that sales calls about the machine were non-stop)
I would second this, and add that it’s in no way expensive ... certainly not OVER expensive. It’s priced right at the bottom end of most large workstations. Albeit the MacPro is only single socket, while offerings from Dell and HP are dual (and I think quad, but I’ve never had to buy anything with four processors in it).
The Mac Pro is selling extremely well for those that need it or find value in it. As I’ve said before, it’s a machine that will last well into and maybe beyond a decade, even with Apple switching to ARM.
