Important vSAN All Flash Caching Sizing Update

There has been a change in the All Flash (only) Write Cache Sizing Guideline.

The short:  10% of intended useable capacity is overally (at times) conservative

The new: Based upon performance levels (see chart below:  Note the below is per Host spec)

  • Still recommend 2 disk groups + / host for better performance
    • So if the sizing is 800GB total / host – use 400GB drives and 2 disk groups per host:  Net is 800GB / host
  • IOPs target in chart is per host as well

See published blog: https://blogs.vmware.com/virtualblocks/2017/01/18/designing-vsan-disk-groups-cache-ratio-revisited/

Note that 600GB+ write cache drives can be useful.  Not in the extra write buffer space but better wear and write spread.  Could help lower latency. See blog for more details.

screen-shot-2017-01-18-at-12-10-48-pm

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