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
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.