Unity Architecture – Part I

Last year, Dell EMC announced Unity midrange storage array at EMC World. Unity is based on VNXe architecture and does not replace the higher model of VNX2, i.e. VNX8000. This post takes a closer look at Unity to understand its hardware components, design, and the software. It is a two-part series. Part I is all about Unity hardware and part II  talks about software architecture of unity.

There are three variants in Unity, Unity Hybrid, Unity All Flash and Unity VSA. The models are Unity 300/300F, 400/400F, 500/500F, 600/600F. Model with “F” at the end is all flash (only SSD’s) and the other one is a hybrid storage system (Flash + Spinning disks). Unity VSA is a virtual appliance that can be deployed on vSphere.  Now let us take a look at some of the important specifications of these models,


The specifications listed here is for a system that runs on Unity OE 4.1 aka Falcon.

Unity 300/300F Unity 400/400F Unity 500/500F Unity 600/600F
Processor 2 x Intel 6-core, 1.6GHz 2 x Intel 8-core, 2.4GHz 2 x Intel 10-core, 2.6GHz 2 x Intel 12-core, 2.5GHz
Memory (Both SP) 48 GB 96 GB 128 GB 256 GB
Minimum/Maximum drives 5/150 5/250 5/500 5/1000
Maximum raw capacity* 2.34 PBs 3.91 PBs 7.81 PBs 9.77 PBs
Max IO modules 4 4 4 4
Max number of pools 20 30 40 100
Max LUN Size 256 TB 256 TB 256 TB 256 TB
Max File System Size 64 TB 64 TB 64 TB 64 TB
Max LUNs per array 1,000 1,500 2,000 6,000

*Maximum raw capacity may vary.

Supported disks

Unity Hybrid

Spinning disk drives

Unity All Flash

Solid state drives used in Unity are of eMLC and TLC type and the disks highlighted in bold are 1 WPD (write per day) disks.

Disk Processor Enclosure (DPE)

DPE holds storage processor (SP), IO modules and disks. Two variants of DPE is available,

  • 25 Drive DPE that can hold 2.5″ disks (Available for hybrid and all flash array)
  • 15 Drive DPE that can hold 3.5″ disks (Only available for hybrid array)

As seen in the table, SP in the respective model will have a different CPU model and a variable amount of memory. Both types of DPE will occupy 2U when mounted on a rack. The first four drives in Unity is DPE is called system drives. These drives contain Unity OE (Operating Environment). Remaining space in these drives can be used for storage pools. A minimum number of disks that are required to initialize system is 5. On the rear side of the DPE we have, 2x Storage Processor (1&2 on image) , 4x onboard converged network ports (Optical/Twinax) (3), 4x onboard 10 GbE Base-T RJ45 ports (4), 2x power supplies (5), IO module slots (6), 4x SAS port for backend connection (7), a management port and a service port (8). Here is the picture of DPE,

Disk processor Enclosure. Image source: emc.com

The onboard Converged Network Adapter (CNA) can be configured for 16/8/4/2 Gbps Fiber Channel SFP’s (multimode and single mode) or 10 GbE optical using SFP+ and Twinax. The other 2 on-board port on an SP is 10 GbE Base-T. All these onboard ports can be configured for Block (FC/iSCSI) or File IO (NFS/CIFS). And in each SP there is a management port (to access Unisphere) and a service port (service use or engineering use).

Each SP can have two IO modules installed to expand front end host connection. IO module installed on SPA should match what is installed on SPB respective slot. There cannot be a miss match. Following are the IO modules that Unity supports,

  • 4 port 16GB Fiber Channel
  • 10GbE Base-T
  • 1GbE Base-T
  • 2 port 10GbE Optical (SFP+ and Twinax)
  • 4 port 10GbE Optical (SFP+ and Twinax)
  • 12Gb SAS for backend expansion (Only for Unity 500 and 600)
Unity supports Active Twinax cables only and no support for Passive Twinax.

Protections space for cache (No Vault)

In the case of storage processor failure, the cache contents are dumped into M.2 SSD that resides inside each SP. If cabinet loses power, Unity SP contains an inbuilt battery backup unit (BBU) that can power the SP long enough to dump cache contents into M.2 SSD. Cache content is restored to respective SP cache when power is restored or SP is replaced. The M.2 SSD also contains Unity OE boot image.

Disk Array Enclosure (DPE)

The DAE holds drives and the number of DAE that a model supports will vary. Please refer to the specification table in the post to know the maximum DAE that a system will support. There are two variants of DAE,

  • 25 Drive DAE that can hold 2.5″ disks (2U)
  • 15 Drive DAE that can hold 3.5″ disks (3U)

On the rear side, each DAE has 4 SAS ports (marked as A & B) for DPE to DAE and DAE to DAE connection. The ports need mini-SAS HD connectors. Here are the images of 15 & 25 drive DAE,

15 drive DAE. Image source: emc.com
15 drive DAE. Image source: emc.com

That’s all about Unity hardware. In the next post, we will take a closer look at software in Unity. Stay tuned! Click here to read part II.

Disclosure: I work for Dell EMC and this is not a promoted post.