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Core Double-Take requirements

Each Double-Take for Windows server must meet the minimum core requirements below. Your servers may need to meet additional requirements depending on the job type will be using. See the requirements section for each of the job types for those specific requirements. Double-Take for Linux servers have separate requirements which are detailed in Full server to ESX appliance requirements.

Operating system—Double-Take for Windows supports Windows 2003, 2008 and 2012, with the following caveats.
- Windows 2003 operating systems require Service Pack 1 or later.
- Server Core 2008 is not supported for any job type.
- Server Core 2008 R2 and 2012 are supported for files and folders, full server, full server to Hyper-V, V to Hyper-V, and agentless Hyper-V jobs but with caveats. See the requirements sections for those job types for Server Core details.
- Hyper-V is supported for full server to Hyper-V, V to Hyper-V, and agentless Hyper-V jobs. See the requirements sections for those job types for detailed Hyper-V requirements.
- There are multiple Double-Take editions that correspond to the various Windows operating system editions. Your reseller or distributor can assist you in selecting the right Double-Take edition for your operating system and protection needs.
- If you are using Windows 2008 Hyper-V R2 with Cluster Shared Volumes (CSV), you can use Double-Take within the guest. However, you will be unable to protect the virtual machines at the host level using Double-Take. Although CSV is not supported for host-level protection for Windows 2008, you can use host-level protection for non-CSV virtual machines on a CSV configured cluster. See Agentless Hyper-V requirements for more information.
- Cluster Shared Volumes (CSV) support at the host-level is for Windows 2012 only.
- Even though the Double-Take for Windows Foundation Edition is for Windows Foundation Server, Small Business Server, Storage Server, and Essential Business Server editions, you can install the Double-Take for Windows Foundation Edition on a server running higher Windows operating systems, so you do not have to pay extra for an upgraded Double-Take license. When the Foundation Edition is installed on a server running higher Windows operating systems, the following limitations will apply. 1) The server will function in a target role only. 2) The target-only server can only protect a source that is running the Double-Take for Windows Foundation Edition and one of the operating system editions listed above. 3) Full server protection is the only supported method of failover.
File system—Double-Take supports the NTFS and ReFS file system. FAT and FAT32 are not supported. For detailed information on other file system capabilities, see Mirroring and replication capabilities.
System memory—The minimum system memory on each server should be 1 GB. The recommended amount for each server is 2 GB.
Disk space for program files—This is the amount of disk space needed for the Double-Take program files. The amount depends on your operating system version and your architecture (32-bit or 64-bit) and ranges from 350-500 MB.

The program files can be installed to any volume while the Microsoft Windows Installer files are automatically installed to the operating system boot volume.

Make sure you have additional disk space for Double-Take queuing, logging, and so on.
Server name—Double-Take includes Unicode file system support, but your server name must still be in ASCII format. If you have the need to use a server's fully-qualified domain name, your server cannot start with a numeric character because that will be interpreted as an IP address. Additionally, all Double-Take servers and appliances must have a unique server name.

If you rename a server that has already has a Double-Take license applied to it, for example if you rebuild a server, you will have to perform a host-transfer to continue using that license. This includes changing the case (capitalization) of the server name (upper or lower case or any combination of case). See Activating a single Double-Take server for details on completing a host-transfer.
Time—The clock on the source and target servers must be within a few minutes of each other, relative to UTC. Large time skews will cause Double-Take errors.
Protocols and networking—Your servers must meet the following protocol and networking requirements.
- Your servers must have TCP/IP with static IP addressing. (Some job types allow you to add DHCP addresses for failover monitoring, although only after a job has already been created. Keep in mind that depending on your failover configuration, a source reboot may or may not cause a failover but having a new address assigned by DHCP may also cause a failover.)
- By default, Double-Take is configured for IPv6 and IPv4 environments, but the Double-Take service will automatically check the server at service startup and modify the appropriate setting if the server is only configured for IPv4. If you later add IPv6, you will need to manually modify the DefaultProtocol server setting. See Server and job settings for details.
- For some job types, IPv4 is the only supported version. See the requirements for each job type.
- IPv6 is only supported for Windows 2008 and 2012 servers.
- If you are using IPv6 on your servers, your clients must be run from an IPv6 capable machine.
- In order to properly resolve IPv6 addresses to a hostname, a reverse lookup entry should be made in DNS.
DNS updates—Some job types allow you to update DNS at failover time. To be able to use DNS updates, your environment must meet the following requirements.
- The source and target servers must be in the same domain.
- At failover time, the target must be able to reach the DNS servers that you want to update.
- For workgroup environments, both the source and target server must be in the workgroup.
- Each server's network adapter must have the DNS suffix defined, and the primary DNS suffix must be the same on the source and target. You can set the DNS suffix in the network adapters advanced TCP/IP settings or you can set the DNS suffix on the computer name. See the documentation for your specific operating system for details on configuring the DNS suffix.
DNS updates are not supported for Server Core servers or NAT environments.
Windows firewall—If you have Windows firewall enabled on your servers, there are two requirements for the Windows firewall configuration.
- The Double-Take installation program will automatically attempt to configure ports 6320, 6325, and 6326 for Double-Take. If you cancel this step, you will have to configure the ports manually.
- If you are using the Double-Take Console to push installations out to your servers you will have to open firewall ports for WMI (Windows Management Instrumentation), which uses RPC (Remote Procedure Call). By default, RPC will use ports at random above 1024, and these ports must be open on your firewall. RPC ports can be configured to a specific range by specific registry changes and a reboot. See the Microsoft Knowledge Base article 154596 for instructions. Additionally, you will need to open firewall ports for SMB (server message block) communications which uses ports 135-139 and port 445, and you will need to open File and Printer Sharing. As an alternative, you can disable the Windows firewall temporarily until the push installations are complete.
See Firewalls for instructions on handling firewalls in your environment.
Windows Management Instrumentation (WMI)—Double-Take is dependent on the WMI service. If you do not use this service in your environment, contact technical support.
Snapshots—Double-Take uses the Microsoft Volume Shadow Copy service (VSS) for snapshot capabilities. To use this functionality, your servers must meet the following requirements.
- Snapshot operating system—Your servers must be running, at a minimum, Windows 2003 Service Pack 1. You should upgrade to Service Pack 2 or later so that several Microsoft patches that address memory leaks in the Volume Shadow Copy service are applied. If you do not have Service Pack 2 installed, you will need to review the patches available on the Microsoft web site and install those that correct the Volume Shadow Copy service memory leaks.
- Snapshot data—Snapshots are taken at the volume level. For example, if your job is protecting D:\data and E:\files, the snapshot will contain all of the data on both the D: and E: volumes. If your job is only protecting D:\data (E:\files exists but is not included in the job), the snapshot will only contain the D: volume.
- Double-Take installation location—In order to enable Double-Take snapshots, Double-Take must be installed on the system drive. If Double-Take is not installed on the system drive, snapshots will be disabled when enabling protection.
- Snapshot limitations—Sometimes taking a snapshot may not be possible. For example, there may not be enough disk space to create and store the snapshot, or maybe the target is too low on memory. If a snapshot fails, an Event message and a Double-Take log message are both created and logged.
  
  There are also limitations imposed by Microsoft Volume Shadow Copy that impact Double-Take snapshots. For example, different Double-Take job types create different snapshot types, either client-accessible or non-client-accessible. VSS only maintains 64 client-accessible snapshots, while it maintains 512 non-client-accessible snapshots. If the maximum number of snapshots exists and another one is taken, the oldest snapshot is deleted to make room for the new one.
  
  Another example is that Double-Take snapshots must be created within one minute because Volume Shadow Copy snapshots must be created within one minute. If it takes longer than one minute to create the snapshot, the snapshot will be considered a failure.
  
  Additionally, Volume Shadow Copy will not revert snapshots of a volume with operating system files, therefore Double-Take is also unable to revert a volume with operating system files.
  
  You must also keep in mind that if you are using extended functionality provided by Volume Shadow Copy, you need to be aware of the impacts that functionality may have on Double-Take. For example, if you change the location where the shadow copies are stored and an error occurs, it may appear to be a Double-Take error when it is in fact a Volume Shadow Copy error. Be sure and review any events created by the VolSnap driver and check your Volume Shadow Copy documentation for details.
- Other snapshot functionality—You can use Volume Shadow Copy for other uses outside Double-Take, for example Microsoft Backup uses it. Keep in mind though that the driver for Volume Shadow Copy is started before the driver for Double-Take. Therefore, if you use snapshots on your source and you revert any files on the source that are protected by your job, Double-Take will not be aware of the revert and the file change will not be replicated to the target. The file change will be mirrored to the target during the next mirroring process.
Clusters—If your job type supports clustering, make sure your cluster meets the following general requirements in addition to any job specific cluster requirements.
- Best practices—You should carefully review Microsoft documentation and resources for properly configuring your cluster before implementing Double-Take on a cluster. The Microsoft TechNet articles Failover Clusters and Installing and Upgrading Cluster Nodes are two resources you can start with. There are many other resources available on the Microsoft TechNet web site.
- Networking—The following networking requirements apply to your cluster.
  - You must have TCP/IP connections between nodes.
  - Multiple networks are recommended to isolate public and private traffic.
  - The private network should be a unique subnet so that Double-Take will not attempt to use an unreachable private network.
  - Your network can contain direct LAN connections or VLAN technology.
  - For Windows 2003, the cluster nodes must be on the same logical IP subnet.
  - For Windows 2003, the maximum round trip latency between nodes should be no more than ½ second.
- Domain—The cluster nodes must be members of the same domain.
- DNS—Forward and reverse lookups must be implemented on the primary DNS server for the cluster name and individual nodes.
- Cluster service account—For Windows 2003 clusters, use the same cluster service account on source and target clusters.
- Double-Take disk queue—Ensure that the disk queue is not on a Physical Disk resource.
- Volumes—The source and target should have identical drive mappings.
- Licensing—Each node in the cluster must have a valid Double-Take Availability activation code.
- Resource registration—In some cases, the Double-Take cluster resources may not be registered automatically when Double-Take is installed. You can manually register the resources by running DTResUtility.exe, which is installed in the \Windows\Cluster directory.
- Third-party storage—Third-party storage resources are not supported.