I’ve been working with many customers over the last several months and found that many are very familiar with HP hardware and just know how to set things up. Others are looking for guidance from VMware on how to configure for VSAN. There are things I’ve discovered that might not be obvious but can help in the VSAN setup. Bear in mind, I am not an HP server hardware expert, so your comments are greatly appreciated.
Before I go too far, there is a bug in the HP async controller driver for the HP 420i that is included in the HP ESXi image. The bug reduces the queue depth to 28, instead of 1020, causing poor performance in VSAN.
Here’s how to check your hosts IO Controller (storage adapter) queue depth:
- Run the esxtop command on the ESXi shell / SSH session
- Press d
- Press f and select Queue Stats (d)
- The value listed under AQLEN is the queue depth of the storage adapter
To resolve, follow these directions to implement the correct driver:
OK, a little background/overview on I/O Controller guidance for VSAN. In general, VSAN recommends disabling Read and Write cache for any I/O Controller. Since VSAN handles Read and Write caching at the software layer, there’s no need to do it at the hardware level. Also, when destaging write cache, we want to ensure that the writes are committed to disk and not in I/O Controller cache.
In the case of the HP P420i, you cannot disable the I/O Controller cache so VSAN recommends setting it to 100% Read which essentially disables Write cache. I recently discovered that you can also selectively pick and choose which disks to enable cache for.