Many are familiar with Backblaze who offers backup for a low subscription fee. They use their own server designs before adopting the EIA standard rack,
Seagate posted a new photo showing a server with 120 dissk in an array This is double the oversized server Bakblaze uses so the racks wold need to be arger.
With a vast number of hard disks, clearly a server could be provisioned with spectacular amount of storage.The 14 TB disk make this server capable of 1.6 PB of raw storage. This gives 13.440 PB per rack with 8 servers in each column. Considering 60,000 ft2 floor space (like a Walmart floor), 18EB can be envisioned which is 264 which is where many 64-bit file systems start to choke.
Seagate and WD have struggled to come up with an alternative to the conventional perpendicular design currently used. The shingled disks were hard to implement due to their requirements. Heat assisted with a laser seems to be the route forward but lab results are still not practical.
SSD capacity has grown but the price per EB is still far more expensive than a row of storage based on hard disks.14 TB disks are about $400 each while the Micron SSD is $3,000 for 15 TB.
The rack system above has 12 columns which is pretty standard. Usually there is some space between the racks so that it is easier to repair machines that fail. Cable management is well handled with rack systems, cables are properly cut to size etc.
Ingress to such a vast amount of storage is a real concern. Internet speeds still fall short of 1 terabit. Vendors now use a small 8 disk box to copy files to and then ship it to the data center where it is copied to the CDN servers.
With large class systems operations like NASA buy this type of hardware frequently to cope with the various projects. Some telescopes generate over 100TB a day of data.
NEED FOR SPEED
Backplanes have long reached 100 gigabit so that servers can communicate rapidly. 100 gigabit switches and adapters are readily available. Finisar has a new 400G transceiver which can make interconnects faster. Other vendors are also coming up with new hardware.