VSAN 6.0 Part 10 – 10% cache recommendation for AF-VSAN

With the release of VSAN 6.0, and the new all-flash configuration (AF-VSAN), I have received a number of queries around our 10% cache recommendation. The main query is, since AF-VSAN no longer requires a read cache, can we get away with a smaller write cache/buffer size? Before getting into the cache sizing, it is probably worth beginning this post with an explanation about the caching algorithm changes between version 5.5 and 6.0. In VSAN 5.5, which came as a hybrid configuration only with a mixture of flash and spinning disk, cache behaved as both a write buffer (30%) and read…

vSphere 6.0 Storage Features Part 8: VAAI UNMAP changes

A few weeks, my good pal Cody Hosterman over at Pure Storage was experimenting with VAAI and discovered that he could successfully UNMAP blocks (reclaim) directly from a Guest OS in vSphere 6.0. VAAI are the vSphere APIs for Array Integration. Cody wrote about his findings here. Effectively, if you have deleted files within a Guest OS, and your VM is thinly provisioned, you can tell the array through this VAAI primitive that you are no longer using these blocks. This allows the array to reclaim them for other uses. I know a lot of you have been waiting for…

Announcing the Virtual SAN 6.0 Health Check Plugin

Today VMware announces the Virtual SAN 6.0 Health Check Plugin, a feature that will check your Virtual SAN configuration, both proactively and re-actively, and highlight any abnormal conditions found in the cluster. This is available to all our VSAN customers right now. Not only does it check the health of the cluster, but it also checks the state of the network, host connectivity, physical disk status, and underlying virtual machine object state. This is a great tool for ensuring that an initial deployment of VSAN or proof-of-concept has been rolled out successful, giving you confidence in your VSAN deployment. It…

vSphere 6.0 Storage Features Part 7: VAAI XCOPY improvements

The more astute of you who have already moved to vSphere 6.0, and like looking at CLI outputs, may have observed some new columns/fields in the PSA claimrules when you run the following command: # esxcli storage core claimrule list –claimrule-class=VAAI The new fields are as follows (slide right to view full output): XCOPY Use Array XCOPY Use XCOPY Max Reported Values  Multiple Segments  Transfer Size ————— —————–  ————– false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                   false                  0 false                  false                  0 false                  …

Virtual Volumes (VVols) – Syslog and Scratch Usage

I had a very interesting query in my recent VVol post on vSphere HA interop. In that post I showed how the VVol datastore could be used for datastore heartbeating. The question then arose when the VVol datastore could be used for other things, such as a syslog and scratch destination. I couldn’t see any reason why not, but just to be sure, I tested it out in the lab. The quick answer is yes, you can use a Config-VVol for syslog, and no, you cannot use a Config-VVol for scratch. If you want to see the steps involved, and…

When and why do we “stun” a virtual machine?

This is a question that seems to come up regularly, but I don’t think it appears in any great detail in external facing documentation. The question is “when do we stun (or in other words, quiesce) virtual machines”, why do we do it, and more importantly, how long can a stun operation take? One of our staff engineers, Jesse Pool, put together some really good explanations around the VM stun operation, which I am leveraging for this post. I took some particular interest in this as I wrote a bunch of snapshot posts recently around Virtual Volumes (VVols) so I…

Virtual Volumes (VVols), vSphere HA and Heartbeat Datastores

I had a few queries recently on how Virtual Volumes (VVols) worked with vSphere HA. In particular, I had a number of questions around whether or not VVol datastores could be used as a heartbeat datastore by vSphere HA. The answer is yes, the VVol datastore can be used for vSphere HA datastore heartbeating. If you want to see how, please read on. I think these queries may have arisen due to the fact that we do not use datastore heartbeating with Virtual SAN (VSAN). Just by way of reminder, the master host in a vSphere HA cluster uses a…