vSAN Storage Policies

Question 1

Primary Level of Failures to Tolerate (PFTT)

Answer 1

This policy defines how many host and device failures a VM object can withstand. For n failures tolerated, data is stored in n+1 location. (This includes parity copies with RAID 5 or 6.) If no storage policy is selected at the time of provisioning a VM, this policy is assigned by default. Where fault domains are used, 2n+1 fault domains, each with hosts adding to the capacity, are required. If an ESXi host isn’t in a fault domain, it is considered to be in a single-host fault domain. The default setting for this policy is 1, and the maximum is 3.

Question 2

Secondary Level of Failures to Tolerate (SFTT)

Answer 2

In stretched clusters, this policy defines how many additional host failures can be tolerated after a site failure’s PFTT has been reached. If PFTT = 1, SFTT = 2, and one site is inaccessible, two more host failures can be tolerated. The default setting for this policy is 1, and the maximum is 3.

Question 3

Data Locality

Answer 3

If PFTT = 0, this option is available. The options for this policy are None, Preferred, and Secondary. This allows objects to be limited to one site or one host in stretched clusters. The default setting for this policy is None.

Question 4

Failure Tolerance Method

Answer 4

This policy defines whether the data replication mechanism is optimized for performance or capacity. If RAID-1 (Mirroring)—Performance is selected, there will be more space consumed in the object placement but better performance for accessing the space. If RAID-5/6 (Erasure Coding)—Capacity is selected, there will be less disk utilization, but performance will be reduced.

Question 5

Number of Disk Stripes per Object

Answer 5

This policy determines the number of capacity devices where each VM object replica is striped. Setting this above 1 can improve performance but consumes more resources. The default setting for this policy is 1, and the maximum is 12.

Question 6

Flash Read Cache Reservation

Answer 6

This policy defines the amount of flash capacity that is reserved for read caching of VM objects. This is defined as a percentage of the size of the VMDK. This is supported only in hybrid vSAN clusters. The default setting for this policy is 0%, and the maximum is 100%.

Question 7

Force Provisioning

Answer 7

If set to yes, this policy forces provisioning of objects, even when policies cannot be met. The default setting for this policy is no.

Question 8

Object Space Reservation

Answer 8

This policy defines the percentage of VMDK objects that must be thick provisioned on deployment. The options are as follows:

Thin provisioning (default value)

25% reservation

50% reservation

75% reservation

Thick provisioning

Question 9

Disable Object Checksum

Answer 9

A checksum is used end-to-end in validating the integrity of the data to ensure that data copies are the same as the original. In the event of a mismatch, incorrect data is overwritten. If this policy is set to yes, a checksum is not calculated. The default setting for this policy is no.

Question 10

IOPS Limit for Object

Answer 10

This policy sets a limit for IOPS of an object. If set to 0, there is no limit.