The U.2 form factor is a 2.5" drive, not larger than it.

"U.2" does not change anything in the mechanical characteristics of a 2.5" drive, it just replaces the SATA or SAS electrical interface with a NVMe electrical interface.

You can mount a U.2 drive in any location intended for 2.5" drives, as long as its height can fit there.

However, 2.5" drives come in various heights. Many laptops and mini-PCs that accept 2.5" drives accept only some of the smaller heights and they do not accept the greater heights, like 15 mm, which are typical for enterprise SSDs and HDDs, regardless whether they have a NVMe, i.e. U.2, or a SAS interface or a SATA interface.

This new high-capacity U.2 SSD has the standard 15 mm height of the 2.5" form factor.

Apparently TDP is 30 watts¹, according to the product brief. I would imagine it's a single PCB with flash chips on both sides then thermally bonded to the aluminum chassis. That should keep all chips at approximately the same temperature. On its own it could be easily air cooled, but with 24 in a 2U chassis you'll be having some decently hefty forced air over the drives.

1. For comparison, an HDD usually comes in around ~10 watts

The transfer rates limit how much each chip can be active at any given time, so a heat-aware writing allocator can pick the least active blocks for the next writes and distribute the heat accordingly. Even if it’s not heat-aware, the tendency will be that the writes will be distributed over as many chips as there are, and so will be the heat generated.

Now, I would LOVE to see this much SLC flash on a direct to bus attachment setting.

Over the past few years the main improvement in SSD capacity has been due to them stacking an ever-increasing number of NAND layers in a single chip, with state-of-the-art SSDs already having over 300 layers.

No need to worry about cooling when each layer in the sandwich is only a fraction of a micrometer thick!

the u.2 form factor indeed evolved from chassis designs that were originally 2.5" drives. It's now kind of becoming obsolete with new designs using things like E1S, E1L (exactly the correct height to be slotted into a 1U server, it's like a slightly wider M.2, but meant to be insertable and removable), and E3S and E3L.

Note that the 245TB is an E3L, the half size version of it come in smaller size.

https://americas.kioxia.com/en-ca/business/ssd/solution/edsf...

https://www.exxactcorp.com/blog/storage/edsff-e1s-e1l-e3s-e3...

https://www.simms.co.uk/tech-talk/e1s-e1l-the-new-server-for...