Capability

Use Case

Value

Comments

Number of disk stripes per object

Performance

Default 1

Maximum 12

This is a standard RAID 0 stripe configuration used to increase performance for a virtual machine disk.

This setting defines the number of HDDs on which each replica of a storage object is striped.

If the value is higher than 1, increased performance can result. However, an increase in system resource usage might also result.

Flash read cache reservation (%)

Performance

Default 0

Maximum 100%

Flash capacity reserved as read cache for the storage is a percentage of the logical object size that will be reserved for that object.

Use this setting only for workloads that must have read performance issues addressed. The downside is that other objects cannot use a reserved cache.

VMware recommends not using these reservations unless it is necessary because unreserved flash is shared fairly among all objects.

Number of failures-to-tolerate

Redundancy

Default 1

Maximum 3

Note: Maximum value is 1 if disk size is greater than 16 TB

Defines the number of host, disk, or network failures a storage object can tolerate. The higher the value, the more failures can be tolerated. When the fault tolerance method is mirroring, for n failures tolerated, n+1 copies of the disk are created, and 2n+1 hosts or fault domains contributing storage are required.

The higher n value indicates that more replicas of virtual machines are made, which can consume more disk space than expected.

When the fault tolerance method is erasure coding, to tolerate 1 failure, 4 hosts (or fault domains contributing storage) are required, and to tolerate 2 failures, 6 hosts or fault domains are required.

Failure tolerance method

(Only available with all-flash vSAN 6.2)

Performance or Capacity

Default:

RAID 1 (Mirroring)

Defines the method used to tolerate failures. RAID 1 achieves failure tolerance using mirrors, which provides better performance. RAID 5/6 achieves failure tolerance using parity blocks, which provides better space efficiency.

RAID 5/6 is only available on all-flash vSAN clusters, and when the number of failures-to-tolerate (FTT) is set to 1 or 2. A value of 1 FTT implies a RAID 5 configuration, and a value of 2 FTT implies a RAID 6 configuration.

IOPS limit for Object

(Only available with vSAN 6.2)

Performance

Default:

0

Defines IOPS limit for a disk. IOPS is calculated as the number of I/Os using a weighted size. By default, the system uses a base size of 32 KB. Thus, by default, a 64 KB I/O represents 2 I/O.

Disable Object Checksum

(Only available with vSAN 6.2)

Override Policy

Default:
No

vSAN uses end-to-end checksum to secure the integrity of data by confirming that each copy of a file is exactly the same as the source file. The system checks the validity of the data during read/write operations, and if an error is detected, vSAN repairs the data or reports the error.

If a checksum mismatch is detected, vSAN automatically repairs the data by overwriting the incorrect data with the correct data. Checksum calculation and error-correction are performed as background operations.

This setting determines whether checksums are calculated for the data being written to the volume or not.

Force provisioning

Override policy

Default:

No

Force provisioning allows for provisioning to occur even if the policy configured cannot be satisfied by the currently available cluster resources.

This is useful if there is a planned expansion of the vSAN cluster, and provisioning of VMs must continue, because vSAN automatically tries to bring the object into compliance as resources become available.

Object space reservation (%)

Thick provisioning

Default 0

Maximum 100%

The percentage of the storage objects that are thick provisioned upon VM creation. The remainder of the storage objects are thin provisioned.

This is useful if a predictable amount of storage will always be filled by objects, cutting back on repeatable disk growth operations for all but new or non-predictable storage use.