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Add new Hosts to existing vSAN cluster with different performance tier disk (SAS <-> SATA)


we have an existing vSAN Hybrid Cluster with the following disks in one DG and we have to expand the vSAN cluster with additional hosts.

1 x HPE 800GB 12G SAS Write Intensive-1 SFF SC, Endurance 14600 TBW, Performance Class E

7 x HPE 900GB 12G SAS 10K rpm SFF (2.5-inch)

HPE currently has some problems providing similar Performance Tier SAS SSD's. They suggest using the folllowing SATA SSD's in the new servers.

HPE 800GB 6G SATA WI-3 SFF SC DS SSD, Endurance: 15200 TBW; Performance Class E


vSAN All Flash Caching Tier
vSAN Hybrid Caching Tier
vSAN All Flash Capacity Tier

Endurance and Performance Classes are comparable, but the type is different (SAS 12G <-> SATA 6GB). VMware does not to advise to mix disk/types in the same cluster, but according to the HCL it should be supported.

Given that the endurance and performance class are the same, what risks/problems might occure? Anybody else that has mixed SSD's/types in the same cluster, any experience?



SAS or SATA interface available Hewlett Packard Enterprise has a full portfolio of 12 Gb/s SAS SSDs. The SAS SSDs transfer data at full duplex (bidirectional) allowing greater I/O bandwidth to alleviate bottlenecks. Additionally SAS uses SCSI commands for error recovery and error reporting, which have more functionality than the ATA command set used by Serial ATA (SATA). Hewlett Packard Enterprise has a 12 Gb/s SAS Expander to scale storage capacity for multi-workload needs. SATA SSDs are great in half-duplex (unidirectional) direct connect scenarios when lower price is a priority.

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Hello pirx666,

The 6Gb/s vs 12Gb/s is unlikely to be an issue as 6Gb/s is generally more than adequate.

I would advise against SATA devices as by default they have a low Queue Depth of 32 which may result in your cache-tier drives being a bottleneck.

The recommendation no not mix&match hardware/disk-groups in this scenario would be due to the potential that if you add hosts with slower disk-groups that these may result in also slowing down the current disk-groups.

What estimates of IOPS/Throughput have HPE calculated for disk-groups with each of these configurations?

What non-SATA options do you have here? NL-SAS, or something slightly smaller/bigger might be a better option than SAS here (size should depend on your disk-groups size though).


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This is a pretty standard problem as disks used in a vSAN cluster gets EOL and you have to replace them with different disk types. The problem is if you have different disk types in the cluster, you will not have consistent performance or availability for any components placed on the new disks. VMware addresses it in the vSAN Design and Sizing Guide (page 7, under Balanced Configuration) and recommends "If the components are no longer available to purchase try to add equal quantities of larger and faster devices.". Basically, as long as the disks are faster and larger, you might not get consistent performance and availability but it will be improved on components placed on the new disks, so the inconsistency is therefore not a problem.

You should look into the exact specs of the new and old disks and ensure that the performance characteristics are better on the new ones.




Hi ,

You can use mixed hard drives with different capacity on nodes , but always better keep same to get full performance .

It is not a big challenge since all writes and majority of reads will be handled by FLASH  , still there will be small variation on performance .

Capacity of Disk , I/O all are co-related  .

You may Refer this # Using differently sized disks in a VSAN environment

RAJESH RADHAKRISHNAN VCA -DCV/WM/Cloud,VCP 5 - DCV/DT/CLOUD, ,VCP6-DCV, EMCISA,EMCSA,MCTS,MCPS,BCFA https://ae.linkedin.com/in/rajesh-radhakrishnan-76269335 Mark my post as "helpful" or "correct" if I've helped resolve or answered your query!
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