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Dell Unity provides multiple options for front-end connectivity, via on-board ports directly on the DPE or optional mezzanine card, and via optional I/O Modules. This section discusses recommendations for the different types of connectivity.
In general front-end ports need to be connected and configured symmetrically across the 2 storage processors (SPs), in order to facilitate high availability and continued connectivity in case of SP failure.
EXAMPLE: A NAS Server is configured so that NAS clients connect via port 0 of the first I/O Module on SPA; therefore port 0 of the first I/O Module on SPB must be cabled so that it is accessible to the same networks.
For best performance, it is recommended to use all front-end ports that are installed in the system, so that workload is spread across as many resources as possible.
EXAMPLE: If configuring the 4-port Fibre Channel I/O Module, zone different hosts to different ports so that all 8 ports across the 2 SPs are utilized; don’t simply zone all hosts to the first port of each I/O Module.
When configured for Fibre Channel, Dell Unity CNA ports and I/O Module ports can be configured with 8Gb or 16Gb SFPs. All Fibre Channel ports can negotiate to lower speeds. 16Gb FC is recommended for the best performance for all non Unity XT models. Unity XT models support up to a 32Gb FC I/O Module when running UnityOS 5.1 or later and is recommended for the best performance on a Unity XT platform. For best performance, the 32Gb FC I/O Module is recommended to be installed in I/O Module Slot 0 of Unity XT systems.
Dell Technologies recommends single-initiator zoning when creating zone sets. For high availability purposes, a single host initiator should be zoned to at least 1 port from SPA and 1 port from SPB. For load balancing on a single SP, the host initiator can be zoned to 2 ports from SPA and 2 ports from SPB. When zoning additional host initiators, zone them to different SP ports when possible, to spread the load across all available SP ports.
Utilize multi-pathing software on hosts connected via Fibre Channel, such as Dell PowerPath which coordinates with the Dell Unity system to provide path redundancy and load balancing.
Dell Unity supports iSCSI connections on multiple 1Gb/s, 10Gb/s, and 25Gb/s (on Dell Unity XT) port options. 10GBase-T ports can auto-negotiate to 1Gb/s speeds. Use the highest speed possible for the best performance. If possible, configure Jumbo frames (MTU 9000) on all ports in the end-to-end network, in order to provide the best performance.
To achieve optimal iSCSI performance, use separate networks and VLANs to separate iSCSI traffic from normal network traffic. Configure standard 802.3x Flow Control (Pause or Link Pause) on all iSCSI Initiator and Target ports that are connected to the dedicated iSCSI VLAN.
Dell Unity supports 10GbE and 1GBase-T ports that provide iSCSI offload. Specifically, the CNA ports (when configured as 10GbE or 1GBase-T) and the 2-port 10GbE I/O Module ports provide iSCSI offload. Using these modules with iSCSI can reduce the protocol load on SP CPUs by 10-20%, so that those cycles can be used for other services. Note that iSCSI offload is not available for Dell Unity XT models.
Utilize multi-pathing software on hosts connected via iSCSI, such as Dell PowerPath, which coordinates with the Dell Unity system to provide path redundancy and load balancing.
Dell Unity supports NAS (NFS, FTP, and/or SMB) connections on multiple 1Gb/s, 10Gb/s, and 25Gb/s (on Dell Unity XT) port options. 10GBase-T ports can auto-negotiate to 1Gb/s speeds. Use the highest speed possible for the best performance. If possible, configure Jumbo frames (MTU 9000) on all ports in the end-to-end network, in order to provide the best performance.
Dell Technologies recommends configuring standard 802.3x Flow Control (Pause or Link Pause) on all storage ports, switch ports, and client ports that are used for NAS connectivity.
Dell Unity provides network redundancy for NAS via Link Aggregation Control Protocol (LACP) and Fail Safe Networking (FSN). Combine FSN and LACP with redundant switches to provide the highest network availability. In addition to redundancy, LACP can also improve performance with multiple 1GBase-T connections, by aggregating bandwidth. LACP can be configured across any Ethernet ports that have the same speed, duplex, and MTU. (Note that LACP cannot be enabled on ports that are also used for iSCSI connections.)
While LACP creates a link aggregation with multiple active links, FSN provides redundancy by configuring a primary link and a standby link. The standby link is inactive unless the entire primary link fails. If FSN is configured with links of different performance capability (such as a link aggregation of 10Gb/s ports, and a stand-alone 1Gb/s port), it is recommended to configure the highest performing link as the primary.
NAS Servers are assigned to a single SP, and all file systems serviced by that NAS Server will have I/O processed by the SP on which the NAS Server is resident. For load-balancing, it is recommended to create at least 2 NAS Servers per Dell Unity system, 1 on SPA, and 1 on SPB. Assign file systems to each NAS Server such that front-end workload is roughly the same for each SP.