Tag Archives: Windows - Page 2

Increased response times on VNX when using Windows 2012

Posted by on July 1, 2014 1 comment

Windows 2012 can cause higher response times on VNX

When Windows 2012 issues Trim or Unmap commands to thin LUNs on a VNX, the Storage Processor response times can increase or may initiate a bugcheck.

As part of disk operations to reclaim free space from thin LUNs, Windows 2012 Server can issue large numbers of the SCSI command 0x9E/0x12 (Service Action/Get LBA Status). This SCSI command results in what is called a “DESCRIBE_EXTENTS” I/O on the VNX Storage Processor (SP.) These commands are used as part of the Trim/Unmap process to see if each logical block address (LBA) that has been freed up on the host’s file system is allocated on the VNX thin LUN. The host would then issue Unmap SCSI commands to shrink the allocated space in the thin LUN, thus freeing up blocks that were no longer in use in the file system. RecoverPoint also issues these same SCSI commands when the Thin LUN Extender mechanism is enabled, which can cause similar performance issues. See knowledge base article KB174052 for more information about the RecoverPoint variation of this issue and how to prevent it.

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the community is about helping each other: partition table lost and found

Posted by on June 11, 2013 No comments

Hardware:

  • 1 Windows 2008R2 server containing 2 HBAs
  • 2 SAN switches
  • EMC VNX-5100
  • 1 LUN presented over 4 paths (2 per HBA)
  • no PowerPath or MPIO, so Windows host sees 4 vdisks and uses only 1 (with the risk of corruption)

Scenario:

After an unexpected reboot the host lost access to the data on the LUN and it seemed as if the vdisk was unformatted or at least corrupted.

  • I checked the VNX, but all 4 paths were available
  • “diskpart” showed the disk, but no volumes, so Windows people thought it was a “SAN issue” (which it wasn’t, of course)
  • I tried enabling MPIO, but by default this host made the LUN (now visible as 1 vdisk instead of 4) read only
  • After disabling MPIO I installed PowerPath (unlicensed) to be sure Windows only sees 1 vdisk instead of 4
  • After the reboot I once again saw 1 vdisk and PowerPath showed 4 paths (of which 2 unlicensed)
  • Still no luck accessing the data

the Community starts here

And here is where it gets interesting. The strength of the community is where you help each other and in this case the customer called me to inform me that since he had nothing to loose anyway he used “TestDisk by CGSecurity” and this tool actually discovers data patterns on disks and in the blink of an eye NTFS was found and the partition could be restored.

No format and restore of an earlier backup was necessary!