Summary

Nomad's single-site download (SSD) feature ensures a download across the WAN only happens once per site. It does this by maintaining information about which subnets are neighbors of each other (accessible on LAN rather than WAN), so that when an elected master considers a download from a DP rather than a peer in its subnet, it can discover which other local subnets already has the package. These subnets are typically at a single customer site, specifically a single geographical location. The sequence below describes what happens during SSD.Nomad SSD uses ActiveEfficiency Server. When a Nomad client downloads a package, it registers this information with ActiveEfficiency enabling a profile to be created on which Nomad clients hold particular packages.

The following Nomad features require ActiveEfficiency:

On this page:

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.

Nomad reacts dynamically to network adapter changes, and if its IP address changes it will automatically update its subnet information in ActiveEfficiency. So, for example, closing the lid of a laptop and moving it to another subnet and resuming work there is handled by Nomad.

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

Using the latest ActiveEfficiency Server version is recommended in order to benefit from these features. ActiveEfficiency Server 1.10 has information on setting up an instance to work with Nomad.

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.

If you have clients on networks where broadcasts are disabled (for example wireless) then enable local SSD by setting SSDEnabled=7. Also set ContentProviderOnWifi=1.

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.

The following points should be noted:

  • On a multi-NIC host, only one NIC gets registered and a wired interface takes precedence over a wireless interface during registration
  • If Nomad fails initially to register an adapter, it retries every 5 minutes (for as long as SSD is enabled) until it succeeds
  • Wireless adapters can be configured to act as SSD content providers and consumers. Use the ContentProviderOnWiFi registry setting to do this
  • If the initial device registration was successful when the Nomad service started but the ActiveEfficiency web service later becomes unavailable, when Nomad subsequently downloads and caches a package it will not be able to register the package with ActiveEfficiency (see below for details). Nomad does not re-attempt package registration, so ActiveEfficiency will not know that this particular Nomad host has the package.

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 you change the host name or domain, Nomad and ActiveEfficiency will regard this as a new computer and generate a new device ID for it.

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.

Registry value

Type

Default

Notes

Installer property

ContentRegSyncCycleHrsREG_DWORD

24

A periodic cycle that does pending content registrations. The value specifies the periodic run of the cycle in HOURS .

Setting it to 0 means the feature is turned off and Nomad will not run the content registration sync cycle.

Range: from 4 hours to 168 hours (1 week).

When this registry value is set to non-zero the feature is enabled, and Nomad sets the following two registry values:

  • ContentRegSyncReqDelay is set to 1000 millisecs
  • ContentRegSyncBatchSz is set to 30

MODULE.NOMAD.CONTENTREGSYNCCYCLEHRS

ContentRegSyncReqDelayREG_DWORD

1000

Delay, in milliseconds, between successive content registration API calls to ActiveEfficiency

Range: from 100 milliseconds to 60000 milliseconds (1 minute).

MODULE.NOMAD.CONTENTREGSYNCREQDELAY
ContentRegSyncBatchSzREG_DWORD

30

Number of content registrations that will be attempted in each content registration cycle.

Range: from 5 to 100 registrations per run.

MODULE.NOMAD.CONTENTREGSYNCBATCHSZ

How it works

The information about sites and their associated subnets are stored and maintained in ActiveEfficiency. When a Nomad client downloads a package, it registers this information with ActiveEfficiency, enabling it to build a profile of which Nomad client holds particular packages and on which subnet. 

Building a download profile in ActiveEfficiency

When a Nomad client on a subnet requires a particular package, it first tries to find a copy on the local subnet using the standard method for retrieving cached Nomad files.

Looking for a package on a local subnet

If no local copy of the package is found it then tries the ActiveEfficiency database to see if any Nomad clients on other subnets at the same site hold a copy.

Searching the ActiveEfficiency profile for a package to download

Only when all other avenues have failed will Nomad resort to downloading the package from the DP over the WAN.

Package downloaded from the DP if not on local subnet or profiled

When the master has a portion of the package it, registers itself with ActiveEfficiency to say that it can provide this package to other subnets if required.

Master registering with ActiveEfficiency

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.

Nomad peers never deal with SSD; they only copy packages from their subnet's master. The subnet master may have the package completely cached or it may be actively downloading from another site or from a DP – the source makes no difference to the peer

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.

All Nomad clients that have SSD enabled will register content download with ActiveEfficiency, not just the subnet master.

If the Nomad client is running as a guest on VMware, it registers itself as DeviceType=0 in ActiveEfficiency. ActiveEfficiency excludes these devices from SSD query results as they are deemed ineligible to provide content.

Architecture and ports

Nomad SSD architecture

Nomad SSD uses the following ports in its communications:

PortsNotes
TCP 80 (HTTP)
TCP 443 (HTTPS)

Step 1

Nomad systems on the branch site register in ActiveEfficiency the content they hold in their shares
TCP 80 (HTTP)
TCP 443 (HTTPS)

Step 2

Nomad Masters get information on which Nomad systems hold specific content

TCP 80 (HTTP) 
TCP 443 (HTTPS)

TCP 139 (SMB)

TCP 445 (SMB over TCP)

Step 3

Nomad Master fetches a package from the registered Nomad share on a neighboring subnet


We recommend that the latest version of ActiveEfficiency is installed to support this feature, please refer to Prerequisites for more details.

Enabling SSD in WinPE

To enable SSD in WinPE:

  1. Edit the task sequence for which you want to use SSD.
  2. Enable Single Site Download.
  3. In ActiveEfficiency URL enter  http://<server_FQDN>/ActiveEfficiency  or  https://<server_FQDN>/ActiveEfficiency  depending on the protocol you are using, where <server_FQDN> is the FQDN of the server or its DNS alias.
  4. Click OK.