I/O alignment in VMWare ESX

In Many cases, VMDK partitions can become misaligned, leading to performance degradation.So before deploying your virtual machine check these recommendation for Netapp

VMDK partitions need to be aligned at both the VMFS and guest OS levels. For example, you can align the partitions at the VMFS level by selecting the vmware LUN type when creating your LUNs. By doing so, the partitions are aligned to sector 128 or sector 0, depending on whether you use VirtualCenter or vmkfstools to create the VMFS. Regardless, the partitions will be aligned as both are multiples of 4KB, thereby fulfilling the WAFL read/write requirements.

However, because of the 63-sector offset implemented by the Windows and Linux operating systems, the partitions will still not be aligned at the guest OS level. Therefore, you must manually align the .vmdks at the guest OS level for VMFS and NFS datastores.

Cause of this problem

Partial writes occur when using VMFS filesystem or NFS based VMDKs on ESX.

This issue is not unique to NetApp storage. Any storage vendor or host platform may exhibit this problem. You can determine if partial writes are occurring by looking at the wp.partial_write setting in perfstat. wp.partial_write is a block counter of misaligned I/O. In Data ONTAP 7.2.1 and subsequent 7G versions, read/write_align_histo.XX and read/write_partial_blocks.XX are also available in the stats stop -I perfstat_lun section of a Perfstat

Aligning your partitions to a 4K boundary in both the VMDK and the LUN is a recommended bast practice (see TR3428 for this and other ESX on NetApp Best Practices).

RDMs are not affected by partial writes as long as the LUN type is set to the RDM OS type.

IF you need more details and fixing this issue using mbralign
NETAPP Knowledge Base

NETAPP Knowledge Base