Oracle has supercharged its 7000 unified storage line, effectively replacing two of the products and expanding the line's performance and capacity dramatically upwards. Users will get more scalability and more performance from the new line. The new products have been rebranded too, and are known as the ZFS Storage Appliance line …
The reason the 7420 uses lower density shelves is aggregate bandwidth. The drives it uses are already slow. Stuffing even more of them into a single shelf with less overall bandwidth would make it pretty much unusable for virtualized workloads. I'm betting it's already on the edge of functionality even with a TB of cache.
Bandwith, there plenty
Each disk shelf has 8 x 6 Gbit connection to controller, which is a lot compared to any other disk system on the market. So bandwith / disk drive is extremely high. while this isquite important for some applications like DWH, it's rarely important to virtualised environments, as IPS and low latency are the first priorities.
7720 uses slighlty beefed up 7420 controllers integrated into an intelligent rack which provides two sides disk slots (back and front), SAS-2 backend, coling and power supply system.
First rack in 7720 system can get 320 data drives + 24 write cache SSD's totalling to 344 drives.
This is a JBOD'less system. Each pre installed storage node takes 32 drives + LCC cards. 2 of the drives can be 0-2 write cache devices.
Hope this helpes
they don't make it easy
First, in regards to your reference to the 7210 in your article of yesterday 9/20 (Oracle promises fresh approach to storage). There was a 7210, but it looks like it got morphed into the J4500 (then X4500, and now X4540), which I think was coded Thumper. You have to look at the System Handbook to see this.
As for the 7720, my take is that it's all pre-packaged (as you've mentioned, a la Exadata, Exalogic, exacetera), and high density to meet "bulk storage and backup requirements". Sure the 7420 scales out farther, but it only gets 384TB in a rack, not 720TB.
It's also very confusing how they package the disks in the shelves for the 7720. If you look down in the data sheet, it says 30 drives per shelf (as opposed to 24 per in the other models), to get the max capacity. If you're thinking 8 shelves (like the 7420), this explains why they say "starting capacities of 240TB", with 1TB drives. It doesn't explain how they get to 720TB, which they say takes 360 drives, which means they're not getting the extra capacity with larger (than 2TB) drives. To get 360 drives in 8 shelves, you have to have 45 drives per shelf. Seriously? I know how they get 30 instead of 24.. the same way they get 12 blades across instead of 10 in the 6048 chassis vs the 6000 chassis.. they customize the rack, and use the space at the sides, and add another column of 6 drives to existing shelves. I think they're actually using 10 shelves in the 7720, with 24x 1TB drives in "modular" shelves, initially. Then V2 will be 30x 2TB drives in "integrated" shelves. The confusion is that 8x30 = 10x24. Now the 7720 starts to look like an altogether different beast.
I think you will find the 7720 cabinet has the disk shelves mounted both front-ward and rear-ward facing....hence the claims of better density than the 7420 on a rack basis. They must be still working out how to scale a 7720 across multiple racks. I do not know how the cooling would work in hot-aisle cold-aisle datacentre.
These devices were obviously completed prior to Brian Cantrill and Adam Leventhal leaving the original 7000 product development team...so it will be interesting to see whether this slows the innovation in these devices (and bug fixing).
drives and cooling
It's interesting you should mention rear-mounted drives. I initially was thinking that, until I looked at the shelf chassis (it's full-depth), which made me re-consider the drive math. The data sheet does mention that the 7720 will use special cooling. Perhaps the rear Cooling Door? I also thought they might use 2.5" drives to get the increased drive count. It does definitely seem like the final design has yet to be attained. Maybe that explains the slightly later release than the other models.