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Software FT Sets Are Not Supported in Microsoft Cluster Server

This article was previously published under Q171052
This article has been archived. It is offered "as is" and will no longer be updated.
The software fault tolerance contained within Windows NT Server (FTDISK)will not be supported in Microsoft Cluster Server (MSCS) 1.0 for clusterdisk resources on the cluster shared SCSI bus. This will include mirrorsets, volume sets, and stripe sets with and without parity. FTDISK willcontinue to be supported for local disk resources.

This includes local disk resources on Windows NT Server Enterprise Editionservers using MSCS 1.0. Examples of using FTDISK for local disk resourceswould include creating an FTDISK RAID 5 stripe set that is used for non-cluster purposes on a server. For example, a customer could choose anFTDISK volume for an application that was not used on a cluster. For MSCSdisk resources on a shared SCSI bus, however, the only RAID supported byMicrosoft is hardware level RAID.

The two key facts about this situation are:
  • MSCS still supports RAID on all disks in a cluster, to protect your data in the event of a disk failure. However, disks on a shared SCSI bus must be protected by hardware RAID, while disks that are local to each server may be protected by either hardware or software RAID.

  • Windows NT Server software RAID is still fully supported for all disks connected to a non-clustered server. The technical reasons that prevent Microsoft from supporting software RAID on shared SCSI disks in a cluster are uniquely related to the way MSCS does server failover.
There are two key technical reasons why FTDISK is not supported on theshared SCSI bus in Microsoft Cluster Server 1.0.

The first reason is that RAID metadata cannot be reliably recovered by MSCSin all server failover scenarios. FTDISK stores metadata information aboutall disk members in the registry on the local machine. (The location ofthis information is HKEY_LOCAL_MACHINE\System\Disk.) Therefore, the onlyway to get to the disk metadata is to mount the file system on the diskmembers. This presents no difficulty with non-clustered servers becausethey, by default, always have access to local storage devices.

However, within a cluster, based on specific failure and boot sequences, there are occasional states where a computer is unable to start with all of the volumes necessary for the FTDISK diskset. In such a case, a data set could be orphaned or rolled to a previous version, because the information needed to identify the disk ownership is contained on the disk that is to be mounted. In a cluster it would be theoretically possible for serverfailures to result in unknown states for disks managed by the currentFTDISK. The inability to safely recover RAID disk state until the diskswere already brought back online could also expose the disk members to thepossibility of data corruption, data loss, stale data, and other problemsfor a given data volume.

The other technical issue preventing support of the current FTDISK forshared SCSI disks in a cluster is the lack of a fully automated method ofrecovery from disk problems. For example, in the event of a failover,CHKDSK would need to be run on the FT volume to assess the integrity of thevolume itself. At this time, there is no automatic means of doing this,leaving the responsibility of running CHKDSK to the user.

For additional information, please see the following articles in theMicrosoft Knowledge Base:
160963 CHKNTFS.EXE: What You Can Use It For

158675 How to Cancel CHKDSK After It Has Been Scheduled
The above information is only relevant to implementing software faulttolerance in Microsoft Cluster Server 1.0. The current FTDISK software RAIDremains a supported, reliable, and excellent disk protection solution forWindows NT Server when running on a single server.
MSCS fault tolerant server cluster

Article ID: 171052 - Last Review: 02/27/2014 10:28:24 - Revision: 2.2

Microsoft Windows NT Server 4.0 Enterprise Edition, Microsoft Cluster Server 1.1

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