VMware Solutions Discussions

DFM Diagnose function show LUN misaligned


We are using a 6040 with VMware Vsphere 4 formatted LUN. The LUN is presented to the VMware Hosts via FC and we are using "VMware' Option as the File System.

When we start Data Fabric Manager use the the 'Diagnose' function on our Gateway it show that a number of LUNs are misaligned.

One of the LUN's has 5 VM's on it so I checked each of these Virtual Machines (Linux and Windows) and each of them are aligned to a number that is equally

divisible by 4096, so the Virtual Machine are correctly Aligned.

What is DFM looking at to think the LUN is not aligned. What else can I check for correct alignment?




NetApp Technical Report 3836, "Performance Diagnosis Using Performance Advisor", explains how the diagnose feature works, and what performance counters each diagnostic check looks at.  For the LUN mis-align check, it checks the unaligned_reads and unaligned_writes counters. If the version of ONTAP is greater than 7.2.1 AND either of the two counters are greater than zero, then the diagnosis is that the LUN is mis-aligned.  A copy of the diagnostic check is shown below.

I'd highly recommend you speak with your assigned NetApp Systems Engineer and you review your configuration. If you're presenting a LUN directly to a virtual machine via RDM, I suspect you need to use that guest O/S as the LUN type, not VMware.  The following post is worth a read as it may apply to your situation.


Description: Unaligned I/O requires the filer to read from or write to more blocks than necessary to perform logical I/O. Unaligned I/O might cause an increase in per operation latency.
Diagnosis category: SAN specific issues
Recommendation: Contact your support engineer.
Resource property condition: Storage system should be running DATA ONTAP 7.2.1 or later

     Threshold 1: lun:unaligned_reads
     Default value: 0
     Description: Name of the counter   

Threshold 2: lun:unaligned_writes
     Default value: 0
     Description: Name of the counter

Algorithm: Existence of unaligned operations when the LUN is receiving I/O indicates misalignment.
Remarks: None


<rule name="LUN Misalignment">

     <rule-type>Counter Threshold</rule-type>






















     <recommendation>Contact your support engineer.</recommendation>