Core Double-Take requirements

Each Double-Take Windows server must meet the minimum core requirements below. Your servers may need to meet additional requirements depending on the job type will be selecting. See the requirements section for each of the job types for those specific requirements.

Operating system—There are different Double-Take editions depending on the operating system you are using. Be sure you have the correct Double-Take edition for your operating system.

Microsoft Server Core 2008 R2 is supported for files and folders jobs, but may have specific requirements or limitations for other job types. Server Core 2008 is not supported for any job type.

Each of the Windows 2003 operating systems require Service Pack 1 or later.

Foundation Edition

Standard Edition

Advanced Edition

Premium Edition

Virtual Guest Edition

Virtual Host Standard Edition

Virtual Host Advanced Edition

Virtual Host Premium Edition

File system—Double-Take supports the NTFS file system. FAT and FAT32 are no longer supported.

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. For Windows 2003, this is approximately 300 MB. For Windows 2008, this is approximately 375 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.

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.

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.
IPv6 is only supported for Windows 2008 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.

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. 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.

NAT support—Double-Take does not support NAT configurations because you must select an actual IP address on your source and target servers for monitoring and routing data. You cannot use external addresses.

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 configuration—If you have related data on different drives on your source (for example, an Exchange database on one drive and related log files on another), snapshots of each drive must be taken simultaneously so that the snapshots for each drive represent the same point in time. However, based on the Microsoft Volume Shadow Copy snapshot technology, different snapshots cannot be taken at the same time. To work around this limitation and guarantee data integrity on the target, you need to create a mount point, thus ensuring that one point-in-time consistent snapshot will be taken of both volumes at once. To create a mount point, create an empty folder on one of the drives. Using the Disk Management tool in the Windows Computer Management applet, remove the drive letter from the other drive. Then create a mount point by selecting Mount in the following empty NTFS folder and specifying the folder you just created. If you have multiple drives, create an empty folder on the drive for each of the other drives and create mount points to each of the folders. When the snapshot is taken of the drive, each mount point will be included in the snapshot. You will need to modify your applications to specify the new location for the files that are now on the mount point. For additional details on creating and using mount points, see your Windows reference manual. For details on modifying your applications, see your application reference manual.
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.