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Understanding vSAN memory consumption in ESXi 6.5.0d/ 6.0 U3 and later (2113954)

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Purpose

This article provides information about memory consumption in the latest version of vSAN 6.2 (ESXi 6.0 Update 3 and later) and vSAN 6.6 (ESXi 6.5.0d and later) and a provides example scenarios.

Resolution

To calculate vSAN memory consumption in these releases, use this equation:

BaseConsumption + 
(NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +
(NumCapacityDisks * CapacityDiskBaseConsumption)
 

Where:

  • BaseConsumption: is the fixed amount of memory consumed by vSAN per ESXi host. 
  • NumDiskGroups: is the number of disk groups in the host, this value should range from 1 to 5.
  • DiskGroupBaseConsumption: is the fixed amount of memory allocated to each individual disk group in the host. This is mainly used to allocate resources used to support inflight operations on a per disk group level.
  • SSDMemOverheadPerGB: is the amount of memory allocated per GB of SSD.
  • SSDSize: is the size of the SSD disk in GB.
  • NumCapacityDisks: is the number of capacity disks in the host (across all the diskgroups).
  • CapacityDiskBaseConsumption: is the amount of memory allocated per capacity disk.

Constants

  • BaseConsumption = 5426 MB
  • DiskGroupBaseConsumption = 636 MB
  • SSDMemOverheadPerGB (hydrid) = 8 MB
  • SSDMemOverheadPerGB (allflash) = 14 MB
  • CapacityDiskBaseConsumption= 70 MB
Note: In these releases, encryption and deduplication features have no impact on memory consumption.

Examples

Let’s look at some working examples where the hosts the SSD size is 600GB each diskgroup has 3 MDs (or data devices for the all flash case).

Example 1: One disk group per host, hybrid configuration:

BaseConsumption + 
(NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +
(NumCapacityDisks * CapacityDiskBaseConsumption)
=
5426 MB + (1 * (636 MB + (8MB * 600))) + (3 * 70 MB)
=
11072 MB


Example 2: Three disk groups per host, hybrid configuration:

BaseConsumption + 
(NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +
(NumCapacityDisks * CapacityDiskBaseConsumption)
=
5426 MB + (3 * (636 MB + (8MB * 600))) + (9 * 70 MB)
=
22364 MB

5426 + (3 * (636 MB + (8 * 600))) + (9 * 70)


Example 3: One disk group per host, all flash configuration:

BaseConsumption + 
(NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +
(NumCapacityDisks * CapacityDiskBaseConsumption)
=
5426 MB + (1 * (636 MB + (14MB * 600))) + (3 * 70 MB)
=
14672 MB


Example 4: Three disk groups per host, all flash configuration:

BaseConsumption + 
(NumDiskGroups * (DiskGroupBaseConsumption + (SSDMemOverheadPerGB * SSDSize))) +
(NumCapacityDisks * CapacityDiskBaseConsumption)
=
5426 MB + (3 * (636 MB + (14MB * 600))) + (9 * 70 MB)
=
33164 MB


Additional Information

Considerations when calculating memory requirements for hosts participating in a vSAN cluster :
  • vSAN scales back on its memory usage when hosts have less than 32GB of memory.
  • vSAN consumes additional memory when the number of nodes in the cluster is greater than 32.
For more information about sizing and designing a vSAN cluster, see:

See Also

Update History

04/07/2017 - Added vSAN 6.5 to Products. 07/31/2017 - Updated KB to only cover memory consumption in the latest vSAN releases (ESXi 6.0 Update 3 and ESXi 6.5.0d).

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