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Q171052: Software FT Sets Are Not Supported in Microsoft Cluster Server

Article: Q171052
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbsetup
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server, Enterprise Edition version 4.0 
- Microsoft Cluster Server 
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SUMMARY
=======

The software fault tolerance contained within Windows NT Server (FTDISK) will
not be supported in Microsoft Cluster Server (MSCS) 1.0 for cluster disk
resources on the cluster shared SCSI bus. This will include mirror sets, volume
sets, and stripe sets with and without parity. FTDISK will continue to be
supported for local disk resources.

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

MORE INFORMATION
================

There are two key technical reasons why FTDISK is not supported on the shared
SCSI bus in Microsoft Cluster Server 1.0.

The first reason is that RAID metadata cannot be reliably recovered by MSCS in
all server failover scenarios. FTDISK stores metadata information about all disk
members in the registry on the local machine. (The location of this information
is HKEY_LOCAL_MACHINE\System\Disk.) Therefore, the only way to get to the disk
metadata is to mount the file system on the disk members. This presents no
difficulty with non-clustered servers because they, 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 server failures to result in
unknown states for disks managed by the current FTDISK. The inability to safely
recover RAID disk state until the disks were already brought back online could
also expose the disk members to the possibility of data corruption, data loss,
stale data, and other problems for a given data volume.

The other technical issue preventing support of the current FTDISK for shared
SCSI disks in a cluster is the lack of a fully automated method of recovery 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 the volume 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 the Microsoft
Knowledge Base:

  Q160963 CHKNTFS.EXE: What You Can Use It For

  Q158675 How to Cancel CHKDSK After It Has Been Scheduled

The above information is only relevant to implementing software fault tolerance
in Microsoft Cluster Server 1.0. The current FTDISK software RAID remains a
supported, reliable, and excellent disk protection solution for Windows NT
Server when running on a single server.

Additional query words: MSCS fault tolerant

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Keywords          : kbsetup 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbAudDeveloper kbClustServSearch
Version           : winnt:4.0
Issue type        : kbinfo

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