Multipath I/O identifies different disks as the same disk in Windows

Symptoms

The code in Microsoft Windows that converts a hexadecimal device ID to an ASCII string may drop the most significant nibble in each byte if the byte is less than 0x10. (The most significant nibble is 0.) This causes different disks to be identified as the same disk by Multipath I/O (MPIO). At the very least, this may cause problems in mounting affected disks. And architecturally, this could cause data corruption.

Resolution

When you apply this hotfix, the conversion algorithm is fixed. Disks that were masked by this issue before you installed the hotfix may be raw disks that still have to be partitioned and formatted for use. After you apply this hotfix, check in Disk Management or Diskpart for previously hidden disks.

Note After you apply this hotfix, you may see unique disks if different disks were identified as the same disk by MPIO. You may have to set appropriate settings for the unique disks that are listed.

Update rollups for Windows 8.1, Windows Server 2012 R2, Windows 8, or Windows Server 2012

This hotfix is also included in the following update rollups.

Note The update rollups fix many other issues in addition to the issue that the hotfix fixes. We recommend that you use the update rollup. The update rollup is larger than the hotfix. Therefore, the update rollup takes longer to download.

For Windows 8.1 or Windows Server 2012 R2

For Windows 8 or Windows Server 2012

Hotfix information

A supported hotfix is available from Microsoft Support. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, go to the following Microsoft website: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must be running one of the following operating systems:

  • Windows Vista Service Pack 2 (SP2)
  • Windows Server 2008 Service Pack 2 (SP2)
  • Windows 7 Service Pack 1 (SP1)
  • Windows Server 2008 R2 Service Pack 1 (SP1)
  • Windows 8
  • Windows Server 2012
  • Windows 8.1
  • Windows Server 2012 R2

For more information, see the following resources:
To apply this update in Windows 8.1 or Windows Server 2012 R2, you must first have update 2919355 installed.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any previously released hotfix.
File information

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

References

Learn about the terminology that Microsoft uses to describe software updates.
Properties

Article ID: 2990170 - Last Review: 19 Mar 2015 - Revision: 1

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