The EF550 base models support 12 SSDs (9.6TB) or 24 SSDs (19.2TB), scaling up to 120 drives (96TB). As with the previous generation, the EF550 is a 2U form factor that is Storage Bridge Bay (SBB) version 2 compliant.
First, the controllers.
The controller’s PCI express Gen 3.0 x8 buses between the processor and external interfaces provide 24 gigabytes per second of internal bandwidth per controller, delivering both the “width” to handle large-block I/O and the “speed” to process large amounts of random, small-block I/O.
Each EF550 controller also provides 12GB of DDR3 SDRAM cache memory via three DIMMS. Its cache is battery-backed and destaged to internal flash upon power loss.
Next, let’s explore connectivity.
For connectivity, the EF550 supports various block protocols including:
- 16Gb FC (OM2, OM3, OS1, and OS2 optical)
- 10Gb iSCSI (optical, twinax passive, and RJ-45 Cat 6)
- 6Gb SAS (copper with Mini-SAS cables)
- 40Gb IB (QSFP+ copper and OM3 optical)
When attaching the EF550 directly to a server, or to switches in a SAN fabric, I/O paths to each controller should be established by having one connection to controller A and the other connection to controller B. This redundancy ensures data availability in the event of a path failure.
Once connected, NetApp leverages Asymmetric Logical Unit Access (ALUA), an industry-standard failover mechanism, to allow server I/O down multiple paths to a volume (via either controller).
Now let’s move to the solid-state drives (SSDs).
The EF550 ships with 800GB mixed-use single-level cell (SLC) NAND SSDs from SanDisk with dual (2) full-duplex interface ports. The EF550 actually leverages the dual-active paths from each controller to every SSD as part of its design.
Each SSD is rated at 10 drive writes per day (DWPD), warrantied up to 5 years, but with an endurance lifetime well over 5 years. Of course, each SSD includes wear leveling, garbage collection, etc. -- designed to eliminate the “write cliff”.
NetApp Engineering specifically chose these SSDs as they employ dynamic and static wear leveling techniques that consider both wear and free space when selecting an erase block for garbage collection. Most of that work happens in the foreground as part of the initial write, based on an ordered list of Erase Blocks with the most free space.
This approach leads to very deterministic and sustainable write performance that does not vary with the recent history of writes (some designs that do background GC can write very fast if left idle for a while, but performance drops dramatically under sustained write loads that deplete the available free space).
SANtricity (its operating system) also tracks the wear life of each SSD and issues an alert if the default thresholds below are reached:
- Average erase count over 80%
- Spare blocks remaining under 20%
Finally, the new EF550 includes support for various RAID levels: 0, 1, 3, 5, 6, 10, and DDP (Dynamic Disk Pool).
EF550 Flash Arrays include SANtricity 11.10 and will be available for quoting/ordering beginning December 16, 2013.