There are several other causes for misaligned I/O. The first is, as Jeff Mohler mentioned, volumes with transaction logs for databases. Transactions can be very small and they are written sequentially, so they can create crazy alignment statistics. One other is when you don’t know exactly how the lun type (-t parameter when creating a lun) and the operating system offset for a partition work together.

I.e. if you use a Windows 2008 server, create a LUN of type “windows” (not “windows_2008”), and partition the LUN with default parameters, you will have misaligned I/O.

Also, if you use a Windows 2003 server, create a LUN of type “windows”, and partition the LUN using diskpart with “create partition primary align=64” (as recommended by most other SAN vendors), you will have misaligned I/O because even though the LUN has the correct OS type, if it not partitioned with a default offset, you will have misalignment.

If you are not using virtualization, NetApp’s LUN type must be set to the OS you are using, AND the partition must be created with default settings, or you will get misaligned I/O. If you are using virtualization, TR-3747 has all the information you need.

Also note that I am talking about _partition_ creation using default settings. Once the partition is created, you are free to format the LUN with any blocksize you like. For instance, for MS-SQL, selecting 4kB or 64kB blocks makes no difference for alignment, but the larger blocksize will yield better performance in SQL.

By the way, from ONTAP 8.0.1+, you can directly check alignment with the “lun show –v” command:

/vol/vol1/qtree1/lun1  300.0g (322126640640)  (r/w, online, mapped)

            Serial#: SKK4gZcq8s/m

            Share: none

            Space Reservation: disabled

            Multiprotocol Type: windows_2008

            Maps: win2008server

            Occupied Size:  809.2m (848465920)   

            Creation Time: Mon May 16 12:35:58 CEST 2011

            Alignment: aligned

            Cluster Shared Volume Information: 0x0

Regards,

Anton van Bohemen

If you have database logs in your VMs, they can create what LOOKS like unaligned IO, but the nature of how the DB logs happen, they are false positives.

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