Without SSD, an elected master for each subnet always accesses a DP, often over a slow or congested WAN, even if a neighboring subnet in the LAN had the requested package. In practice, this had no major impact on WAN traffic as Nomad only uses a proportion of the current free network capacity rather than the total rated capacity, but efficiency can be improved by enabling access to Nomad caches on other subnets.

When a Nomad client requires a particular package, it attempts to find a copy on the local subnet. If it is unable to find one, it queries ActiveEfficiency to see if there are Nomad clients on adjacent subnets that hold a copy. If it finds one, it will download the package from it; if it doesn't, it will download the package from the DP over the WAN as a last resort.

The following is how SSD interacts with other Nomad features:

• SSD works seamlessly with FanOut – FanOut applies to peers and SSD applies to subnet masters
• SSD must be enabled in order to use the Integrating with WakeUp feature
• SSD will use IP addresses if P2PEnabled registry value is set to use net literal names
• Work rates only apply to downloads from a DP not to P2P transfers, therefore they do not affect downloads from peers when using SSD
• When packages are purged from the cache, the corresponding entries are deleted from ActiveEfficiency. If you delete content directly from the cache, Nomad will not be aware that it has been removed and the corresponding ActiveEfficiency record will not be deleted. If that host subsequently becomes a site master, it will inform requesting Nomad clients that it does not have the package, forcing them to request the package from the next master in the list.

The following restrictions apply:

• The mechanism does not support alternate source copy downloads, such as downloading an older version of a package from a LAN neighbor then filling in the changes
• Only the initial 0% downloaded of a package and the final percentage (which can be < 100% if the entire package cannot be downloaded) are registered with ActiveEfficiency. There are no "10% so far" etc. intermediate records
• Even if a computer has multiple NICs, only details of one NIC and its subnet are used for SSD. If that NIC is unavailable, SSD will not work properly (although Nomad itself may be working correctly, using the DP rather than another site)
• Remote differential compression integration is not supported over SSD, it will not be used when a subnet master is copying from a site master
• IPv6 is not supported

Site and Local SSD

In version 6.1.100 the local SSD feature was introduced to supplement site SSD for clients on networks such as wireless where broadcasts are disabled, to prevent each client becoming its own master and downloading direct from the DP. In a SSD enabled environment, a master queries ActiveEfficiency to get a list of devices on other subnets within the site that have content. With local SSD enabled, the master also queries for devices having content within local subnet. If any local peers with content are available, then the master downloads from them, otherwise it attempts to download from Site peers (other subnets in the site), and if the master still cannot find any peers, it downloads the content direct from the DP.

In version 7.0 and later, a master skips using local SSD if it sees broadcast messages from peers. This means clients in mixed network environments can be configured with the same SSDEnabled setting (with Local SSD enabled) and clients can move seamlessly between networks. When on a wireless network (where broadcasts are typically disabled) local SSD can be used. On LAN networks (where broadcasts are typically allowed) local SSD would be skipped because a master is elected and sees broadcast activity from peers.

Configuration

Before enabling Nomad clients to use SSD, you need to ensure the following:

• ActiveEfficiency v1.9.700 or later is installed and running successfully. The latest version is recommended: ActiveEfficiency Server 1.10
• The ActiveEfficiency database is populated with information about sites and their associated subnets

High-level overview of how to enable Single Site Download (SSD)

The following information applies to both new and existing installations of Nomad. 

1. Make sure that 1E ActiveEfficiency is installed in your environment and is used as a content location metadata repository.  You can view further information here:  ActiveEfficiency Server 1.10.
2. Within ActiveEfficiency, populate the SSD sites and subnet information.  A sample PowerShell script called PostADSitesandSubnets.ps1 is included in the Nomad installation files, which reads sites and subnets from AD.
3. If not configured already, modify HKLM\Software\1E\NomadBranch\ActiveEfficiency\PlatformURL to http://<servername>/ActiveEfficiency, where <servername> is the FQDN of the server where ActiveEfficiency is installed.

4. Enable SSD on all Nomad agents, by modifying HKLM\Software\1E\NomadBranch\SSDEnabled to 3.  This will enable SSD for both "Provide" and "Consume" modes, specifically Nomad will provide content to other peers and consume content from other peers.

5. If you already have Nomad installed and are only now enabling SSD, then ensure HKLM\Software\1E\NomadBranch\ActiveEfficiency\ContentRegistration is set to 1. In other words Nomad will register downloaded content with ActiveEfficiency, this is automatically enabled for new installations of Nomad and SSD.

Building a subnet profile in ActiveEfficiency

For ActiveEfficiency to build a subnet profile for SSD and the peer backup assistant feature, Nomad must communicate with its web service. When the Nomad service starts, it connects and registers the hosting device by name with ActiveEfficiency which returns a device ID in the form of a GUID that enables it to uniquely identify the Nomad client and its default subnet.

If it is unable to communicate with the ActiveEfficiency web service, it retries every 5 minutes until it succeeds (as long as SSD is enabled). An attempt to communicate with ActiveEfficiency is also made prior to a package download to register its status.

Configuring the Single-Site Download feature in the ActiveEfficiency documentation takes you through the setup process. There are also example PowerShell scripts for retrieving information about sites and their associated subnets from the AD and how to add these to ActiveEfficiency. Information about sites and subnets are typically obtained from the AD but you are free to get this information by other means.

Please refer to Enabling SSD in WinPE to make use of Nomad SSD in OS Deployment.

Uninstallation, reinstallation, and reactivation

When you uninstall Nomad all its registry values are deleted. However, if you subsequently reinstall it, the device ID returned when Nomad next registers with ActiveEfficiency is one that is recycled from the database – this is because that is the device registered for the named computer so it recognizes that the same computer is involved and restores the previous values to the registry.

If a cached package is reactivated, such as after an OSD upgrade or cloning, Nomad will register the package with ActiveEfficiency. (If this is a re-registration, the ActiveEfficiency record is effectively unchanged).

Improved resilience of content registration

The Content Registration Sync Cycle is available in Nomad 7.0 or later (1E Client 4.1 or later) which registers pending and failed content registrations with ActiveEfficiency. 

Registrations can fail when ActiveEfficiency or the SQL Server hosting ActiveEfficiency DB is busy, overloaded or down for maintenance, resulting in content registration mismatch between the clients and ActiveEfficiency.

The following are registry settings used by the Content Registration Sync Cycle feature.

How it works

Fetching content

When Nomad receives a request to download content, an election takes place for a master. The master queries ActiveEfficiency about neighboring subnets (accessible on LAN rather than WAN) so that it can download content from a peer in an adjacent subnet (within the same location) if that content is not available on a peer in its own local subnet. For each subnet, the top 10 Nomad clients (in terms of percentage cached by the Nomad client) are listed – the subnet containing the master is excluded from the list if no peer has the content. During this process, the percentage specified by the requesting client is ignored. Although neighboring Nomad clients may have a lower percentage than the requesting Nomad client, they may in fact have gained more since they last communicated with ActiveEfficiency, so they are potentially useful sources for the package, hence the top 10 rule.

The master (now a subnet master) iterates through the list (which is sorted by percentage) and sends a package status request to each Nomad client. If it receives a response, the master attempts an SMB peer-to-peer download from that Nomad client (the current site master). If the attempt fails (it is not contactable or the limit on the number of concurrent connections is exceeded), it tries the next one in the list. If it fails to get the package from any of them, it downloads from the DP. If the list is empty, the master downloads from the DP. Nomad clients with a lower percentage of the package than the Nomad client requesting it will not respond.

If a download is interrupted part way through (i.e.: the source becomes unavailable), Nomad iterates through the remainder of the list and if it fails to get the package from any of them, it downloads form the DP.

When a download starts, Nomad registers the progress with ActiveEfficiency (0% of the content has been downloaded) and when it finishes, the final percentage is also recorded. As long as the content downloaded is greater than 0%, the host becomes a candidate for another client until the package is deleted from its cache. Records with status of 0% downloaded are purged from ActiveEfficiency.

Architecture and ports