https://ifworlddesignguide.com/entry/281015-poweredge-r740xd... super interesting design.

That is really interesting ...

We deploy our storage with a 2U "head unit"[1] that has the actual computer and all of the SSDs for boot and SLOG and L2ARC and "zfs special"[2] devices. Then we attach 60-drive JBODs externally to those "head units".

With this dual-front design you could have 24 2.5 drives in the first row and 12 3.5 drives in the second row and that would really be helpful when we sometimes need to quickly spin up an adjacent zpool without attaching another whole JBOD.

Sadly, I do not see any configurations with 2.5" drives on the Dell config page:

https://www.dell.com/en-us/work/shop/dell-poweredge-servers/...

If one row was 24x 2.5 drives and the other was 12x 3.5 drives I think we would start deploying these immediately ...

EDIT: Huh ... even the two, rear, boot drives are 3.5" which is sort of weird and gratuitous ...

[1] https://www.supermicro.com/en/products/chassis/2U/216/SC216B...

[2] Yes, it's actually called that ...

That looks like 13 drives per U (26 in 2U); weren't the BB pods 15 drives per U (60 in 4U)?

Up to Storage Pod 5.0 they used 45 per 4U, 6.0 was 60 indeed but it was hanging out from the rack so it is understandable no major OEM has a chassis like that. 52 serviceable drives is not bad at all.