Hello eduruizblas
While the configuration you outlined is okay, whether it is optimal (or adequate) for the workload intended to run on it is another story. A couple of things to note would be that the max that will actually actively be used for Write-cache in an All-Flash configuration is 600GB per Disk-Group - anything more than that is used for extending the lifespan of the device, if you are using modern NVMe (e.g. P4800x) these have an incredibly high TBW anyway so I wouldn't consider spending the extra money on a 960GB over a 600GB model offering much benefit.
Designing vSAN Disk groups - All Flash Cache Ratio Update - Virtual Blocks
What would almost certainly benefit more would be buying 2 cache-tier devices (e.g. 2x400GB or 2x600GB) and configuring 2 smaller Disk-Groups instead of one large one - note that the recommendations in the article above are based on 2x Disk-Groups as this outperforms a single Disk-group of equivalent size and cache:capacity ratio. Going with 2 Disk-Groups may also allow for ease of expansion at a later point. Do note as my colleague Hareesh mentioned, do pay attention to device stats, there can be a massive difference in performance between devices which are both "NVMe" or "SSD", this is merely a device format and doesn't automatically indicate the performance capabilities (and what type of workload it is optimised for), e.g. better HDDs may outperform lower-end SSDs and higher-end SSDs may outperform lower-end NVMe etc.
If you want to configure a 2+2+1 cluster you will need Enterprise vSAN licensing regardless of whether they are 100 metres or 100km from one another.
Bob
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