Starting with OE version 4.4, ports can be configured for a custom MTU size 1280 through 9216. Previously, the MTU sizes were limited to either 1500 or 9000. The custom MTU size can be configured on ports that are used for NAS server, replication, and import interfaces. Any ports that have iSCSI interfaces created must still use 1500 or 9000. Ports with custom MTU sizes configured can be used for link aggregations and fail-safe networking (FSN) if the MTU size matches on all ports. This feature enables Dell Unity systems to be used in complex environments where customized MTU sizes are required.
High availability
On Dell Unity systems, both SPs can be used simultaneously so no dedicated standby hardware is required. The peer SP acts as a hot standby, which actively services I/O but is also ready to take over additional resources if necessary. For example, if SPA fails, the NAS servers along with their file systems fail over to SPB. There may be a short interruption to host access during this operation.
In file environments, NAS servers include one or more network interfaces that are created on one or more Ethernet ports for host access. Link loss can be caused by many environmental factors such as cable or switch port failure. In case of link loss, the system does not initiate a failover of the NAS server to the peer SP. Therefore, it is important to configure high availability on the ports to protect against these types of failure scenarios.
Link aggregation combines multiple physical network connections into one logical link. This provides increased bandwidth by distributing traffic across multiple connections and provides redundancy in case one or multiple connections fail, depending on the configuration. If connection loss is detected, the link is immediately disabled, and traffic is automatically moved to the surviving links in the aggregate to avoid disruption. The switch should be properly configured to add the ports back to the aggregate when the connection is restored. Although link aggregations provide more overall bandwidth, each individual client still runs through a single port. Dell Unity systems use the Link Aggregation Control Protocol (LACP) IEEE 802.3ad standard.
Link aggregations can be configured with two to four ports. Starting with OE version 4.2.1, link aggregation can be created using ports from different I/O modules and between I/O modules and the onboard Ethernet ports. Previously, only ports belonging to the same I/O module or onboard Ethernet ports could be aggregated together. All ports within the aggregation must have the same speed, duplex settings, and MTU size.
Link aggregation can be used for NAS server, replication, and file import interfaces. Link aggregation is not supported for iSCSI since multipathing is used for block access. Any ports that have iSCSI interfaces created on them are not listed as options when creating a link aggregation. Also, link aggregations devices are not listed as options when creating iSCSI interfaces.
Starting with, OE version 4.2.1, fail safe networking (FSN) is available. FSN is a high availability feature that extends link failover into the network by supporting switch-level redundancy. FSN appears as a single link with a single MAC address and potentially multiple IP addresses. FSN can consist of Ethernet ports, link aggregations, or any combination of the two. FSN can be created using ports from different I/O modules and between I/O modules and the onboard Ethernet ports.
FSN adds an extra layer of availability to link aggregations alone as link aggregations provide availability in the event of a port failure while FSN provides availability in the event of a switch failure. Each port or link aggregation is considered as a single connection and only the primary port or link aggregation in an FSN is active at a time. All ports in an FSN must have the same MTU size, but the speed and duplex settings can vary.
If the system detects a failure of the active connection, it automatically switches to the standby connection in the FSN. That new connection assumes the network identity of the failed connection, until the primary connection is available again. You can designate which connection is the primary connection at creation time. To ensure connectivity in the event of a hardware failure, create FSN devices on multiple I/O modules or onboard ports. The FSN components can be connected to different switches and no special switches are required. If the network switch for the active connection fails, the FSN fails over to a connection using a different switch, thus extending link failover out into the network.
For more information about high availability and redundancy, reference the Dell Unity: High Availability white paper on Dell Technologies Info Hub.