Disk Alignment for RDMs?

[eagleh]

Hi there,

Recently I have read some articles about disk alignment in order to improve I/O performance. I am wondering how that would be applied to RDMs (Raw Device Mapping). We have a HP EVA, quite a few RDMs are mapped as data drives presented to our VM servers on ESX hosts. I understand if we generate VMFS partitions from VI Client, the partitaions will be aligned to the SAN automatically which I have proved by running "esxcfg-vmhdadevs". But what about RDMs? How to align RDMs?

Much appreciated.

[a_p_]

The alignment of the VMFS partition is done by the vSphere Client automatically (32 kB before vSphere 5.x, 1,024 kB with vSphere 5.x). What needs to be done by yourself is the alignment within the guest OS itself. Starting with Vista, Microsoft aligns the first partition to 1,024 kB. Before that the alignment was 63 blocks (63 x 512Bytes = 31,5kB). Aligning on the OS level is the same for virtual disks as for RDMs. If you are running an older guest OS which does not do proper alignment, you may need to use a disk partitioning tool or boot the VM from e.g. a Windows 7 ISO image into recovery mode and create the partitions using diskpart with the "align=1024" option.

André