Tuning ESX(i) for better storage performance

Many applications are designed to issue large I/O requests for higher bandwidth. ESX/ESXi 3.5 and ESX/ESXi 4.x support increased limits for the maximum I/O request size passed to storage devices. These versions of ESX pass I/O requests as large as 32MB directly to the storage device. I/O requests larger than this are split into several, smaller-sized I/O requests.

Some storage devices, like the EVA, have been found to exhibit reduced performance when passed large I/O requests (above 128KB). As a fix for this, you must lower the maximum I/O size ESX allows before splitting I/O requests.

To reduce the size of I/O requests passed to the storage device using the VMware Infrastructure/ vSphere Client:

  1. Go to Host > Configuration.
  2. Click Advanced Settings.
  3. Go to Disk.
  4. Select Disk.DiskMaxIOSize.
  5. Change value to 128.

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