This article provides the basic introduction of Symmetrix Federated Tiered Storage, including main functions, components and useful whitepapers links.
Federated Tiered Storage (FTS):
FTS is a new and free feature available with Enginuity 5876. This feature allows VMAX 20K and VMAX 40K arrays to use the storage capacity of an external array, no additional hardware is required to enable the feature. FTS allows LUNs that exist on external arrays to be used to provide physical storage for Symmetrix VMAX. The external LUNs can be used as raw storage space for the creation of Symmetrix devices in the same way internal Symmetrix physical drives are used. These devices are referred to as eDisks. Data on the external LUNs can also be preserved and accessed through Symmetrix devices. This allows the use of Symmetrix Enginuity functionality such as local replication, remote replication, storage tiering, data management, and data migration with data that resides on external arrays.
FTS is implemented entirely in Enginuity and does not require any additional Symmetrix hardware. Connectivity with an external array will be established through the same fiber optic SLICs currently used for configuring FAs and RFs. Instead of running FA or RF emulation, however, the processors will run a new type of emulation.
Disk eXternal (DX) Eumulation:
FTS is implemented through a new director emulation called Disk eXternal Emulation. DX emulation is a specialized back-end DA emulation to handle SAN attached disks. DX Directors are configured on existing Symmetrix Front-end Fibre Channel ports and are required to be implemented in pairs for high availability.
Each DX pair can maintain up to two SCSI paths totaling four paths per eDisk per engine for high availability. Only one path is active and the path selection is not configurable. Initiator failover is supported. The configuration process ensures that eDisk ownership is automatically balanced across the peer directors. In this example, DX director 8E and 7E form a DX director pair with a total of 4 ports.
The external LUNs are federated to the Symmetrix array is eDisks. eDisks are added to a new disk group type called an external disk group , then are added to an unprotected Virtual RAID group. Just like Symmetrix internal disks, eDisks are divided into hypers and provisioned as logical volumes. However, logical volumes created from eDisks do not have Symmetrix RAID protection. RAID protection is configured on the external array.
There are two different types of eDisks, Externally Provisioned and Encapsulated.
Externally Provisioned eDisks are external LUNs that have been repurposed for traditional storage use within the Symmetrix. Externally Provisioned eDisks can be allocated as a FAST storage tier and integrate with enterprise features. LUNs to be Externally Provisioned should not contain exiting data as data is deleted on the external LUNs when federating them as Externally Provisioned eDisks.
Encapsulated eDisks are external LUNs that contain existing data prior to being federated to Symmetrix as eDisks. Data is retained (data is not deleted) when federating the LUNs as an Encapsulated eDisks. Volumes which are automatically created from these eDisks cannot be used in a FAST tier with FAST VP, but can integrate with many enterprise features.
Virtual RAID group:
Virtual RAID group is an unprotected, virtual RAID group gets created for each eDisk that gets added to the system. The RAID group is virtual because eDisks are not protected locally by the VMAX; they rely on the protection provided by the external array.
FTS Deployment Figure:
The first step in configuring FTS is to enable DX emulation on at least two directors. Each DX director is configured with a pair of DX ports which are used to connect to external storage arrays. Next, the DX ports are physically connected to the SAN and then zoned to the external array front-end ports (storage ports). Once zoning is complete, LUN mapping and masking should be used on the external array to present the LUN(s) to the proper DX ports. The LUN(s) are mapped through multiple frontend processors on the external array for high availability. The external LUN(s) must have at least 4 logical paths.
Useful FTS Whitepapers:
Author: Fenglin Li
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