NetApp Storage Subsystem Design: Nuts and Bolts

Part 3 of a 5-part series on choosing media for NetApp FAS storage


By Tushar Routh, Sr. Manager, Storage Products, NetApp


In my previous posts in this series I looked at HDD and SSD technology and discussed where they are today and where they’re going. This time I want to focus on underlying infrastructure: shelves and interconnects. Admittedly, these may not seem like the most exciting components, but they play a critical role in delivering availability, in how you deploy storage, and in how your storage is serviced, primary considerations when planning your storage subsystem.


Disk Shelves

NetApp currently offers a line of four shelves for FAS systems. All these shelves are serviceable from the front regardless of location in the rack for easy serviceability, and all are designed to be highly reliable with no single points of failure. On all shelves, shelf firmware upgrades are non-disruptive and alternate control path (ACP) provides out-of-band management.


All our shelves are SAS based:


DS2246. The DS2246 is our performance-and power-optimized shelf that packs 24 drives in only 2U of rack space using small form factor (SFF) drives. Compared to the DS4243 disk shelf, the DS2246 doubles the storage density, increases performance density (IOPS per rack unit) by 60%, and reduces power consumption by 30% to 50%.


DS4246. The DS4246 provides a balance between performance and capacity. It is 4U high and supports 6Gb/sec SAS connections. It can be configured with either 24 large form factor (LFF) high-capacity disk drives or a combination of SSDs and high-capacity disk drives to support Flash Pool configurations.


DS4243. The NetApp DS4243 is 4U high and supports up to 24 hard disk drives (high capacity or high performance) with 3Gb/sec SAS connection.


DS4486. The capacity-optimized DS4486 holds 48 high-capacity disk drives. This disk shelf uses a tandem disk carrier to enclose twice as many LFF disk drives in 4U of rack space. The rack can be supported by a raised floor in a traditional data center. Because of weight, the drives for all dense shelves ship separately. The tandem carrier cuts installation time in half.




NetApp believes that SAS offers significant benefits for the foreseeable future. Today’s 6Gb/second SAS connections deliver more than adequate bandwidth, and the SAS-3 standard offering 12Gb/sec is coming.


The only limitation of SAS is the relatively short run length of the standard copper cables. NetApp is developing a family of optical SAS products to address this problem— the first in the storage industry to do so. Optical cabling will address two main issues:


  • Cabling Limitations. In a crowded data center it can be tough to stay within the 20M SAS cable limit. With much longer cable runs, optical SAS fixes this problem; you can add new disk shelves wherever you have rack space available.
  • Stretch MetroCluster. A stretch MetroCluster lets you mirror data between data centers in separate buildings on the same campus. With optical SAS, you can span up to 500M distances without using a fibre channel to SAS bridge, making optical SAS cheaper and more convenient.


Shelves and Interconnects: Wrap Up

When it comes to deploying storage, shelves and interconnects are the building blocks. Choosing wisely will allow you to deploy a variety of media options while keeping your storage footprint and energy bill low and availability and flexibility high.


The DS4243 shelf will be phased out over time, and we may consider a non-redundant shelf design for archive disks, but otherwise NetApp is pretty happy with its lineup of disk shelves. On the interconnect side, we’ll be continuing our commitment to SAS and expanding optical SAS offerings.

In the next post, I’ll look at a few guidelines for storage deployment.




If faster connections to disk shelves are coming, does that mean that the FCP connections from the filer to hosts will be upgraded from 4Gb/s to 8Gb/s?

All current FAS models already support 8Gb/sec Fibre Channel (with the exception of the FAS2220).

  • The FAS6200 series supports 8Gb/sec for all FC ports.
  • The FAS3200 series includes 4 onboard 4GB/sec FC ports, but 8Gb/sec ports can be added via expansion cards.
  • The FAS2240 supports 8Gb/sec FC ports through the addition of a mezzanine card.