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  • 1.  question of all flash config

    Posted Aug 07, 2019 04:05 PM

    good! I am thinking of setting up a stretched cluster of 4 nodes all flash and I have doubts about the maximum size of the cache disk.
    The idea is to mount a disk group per node with 960 GB of cache and 5 disks of 1.92 Tb SSD.

    Would this configuration be possible?


  • 2.  RE: question of all flash config

    Broadcom Employee
    Posted Aug 08, 2019 02:44 AM

    Hello @eduruizblas

    Yes The configuration that you are planning for 1x 960GB Cache with 5x 1.92TB capacity looks good . Please make sure you understand the type of workload you are about to run and make choice on the CLASS of drive matters . We have drive class from Class-A (30000 IOPS) capability to Class-F (100,000 IOPS) Capability , also the protocol 3D-xPoint , NVMe , SAS ..etc . Make sure you choose the right hardware for the types of application you are about to run .

    Example : You can have all NVMe Setup , NVMe Cache with SAS capacity setup ,  all SAS setup , NVMe Cache with Sata capacity etc .


    Hareesh K G

  • 3.  RE: question of all flash config

    Posted Aug 08, 2019 04:38 AM

    First of all, thanks for the reply.
    The idea is to mount nvme for cache disks and mixed use sas for capacity disks.

    Another question do I necessarily need the enterprise license for this config? I don't need to activate compression and dedup.

    The configuration would be as follows:
    2 nodes in one room and another 2 in a different one, with a third quorum room. The distance between both rooms does not exceed 100 meters but I need fault tolerance of a complete room

  • 4.  RE: question of all flash config

    Posted Aug 08, 2019 06:03 AM


    Based on your configuration, it will be a stretched cluster. and as per the below you need the enterprise license:

    and for more info please find the VSAN license guide: https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/products/vsan/vmware-vsan-66-licensing-guide.pdf

  • 5.  RE: question of all flash config
    Best Answer

    Posted Aug 08, 2019 09:07 AM

    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.



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  • 6.  RE: question of all flash config

    Posted Aug 08, 2019 09:56 AM

    thanks for the reply In case of using a configuration of two vsan cluster 1 + 1 + 1 and 1 + 1 + 1; being one of them all flas and another hybrid. (for saving the project) could you use the standard licenses for this design? regards

  • 7.  RE: question of all flash config

    Posted Aug 08, 2019 01:36 PM

    As per the licensing documentation Standard license should be fine (whether properly stretched across sites or in same building):

    Scenario 13: 1 host + 1 host+ witness (2-node cluster) across 3 rooms in the same building with maximum 25 VMs This scenario requires either 1 vSAN STD for ROBO (per-VM 25-pack) or 4 vSAN STD per CPU licenses.

    Scenario 14: 1 host + 1 host + witness (2-node cluster) across physical sites with maximum 25 VMs This scenario requires either 1 vSAN STD for ROBO (per-VM 25-pack) or 4 vSAN STD per CPU licenses. Customer does not require ENT licenses for a 2-node cluster stretched across 2 physical site.