Table of Contents
Question
What is the minimum number of VxRail nodes required for a vSAN storage policy with RAID-6 (Erasure Coding)?
A. 4
B. 5
C. 6
D. 7
Answer
C. 6
Explanation
The minimum number of VxRail nodes required for a vSAN storage policy with RAID-6 (Erasure Coding) is 6.
RAID-6 is a data protection technique that uses a parity scheme to store data across multiple disks. This allows vSAN to tolerate the failure of up to two disks without losing data. However, RAID-6 requires more disks than RAID-1 (mirroring) to achieve the same level of protection.
In order to use RAID-6 with vSAN, you must have at least 6 nodes in your cluster. This is because each node must have at least 2 disks available for data storage. The remaining disks can be used for caching or for storing system logs.
If you have fewer than 6 nodes in your cluster, you can still use RAID-5 with vSAN. RAID-5 requires fewer disks than RAID-6, but it does not provide the same level of protection.
Here is a table that summarizes the requirements for different RAID levels with vSAN:
| RAID Level | Minimum Number of Nodes | Data Protection |
|---|---|---|
| RAID-1 | 2 | Data loss if 1 node fails |
| RAID-5 | 4 | Data loss if 2 node fails |
| RAID-6 | 6 | Data loss if 2 node fails |
A vSAN storage policy defines the availability, performance, and efficiency of the virtual machines (VMs) that use vSAN storage. A storage policy consists of one or more rules that specify the desired level of service for the VMs. One of these rules is the failure tolerance method, which determines how vSAN protects the VM data from disk or host failures.
RAID-6 (Erasure Coding) is one of the failure tolerance methods supported by vSAN. It is a technique that splits the data into multiple segments and adds parity information to each segment. The parity information allows the data to be reconstructed in case of a failure. RAID-6 (Erasure Coding) can tolerate up to two simultaneous failures without losing data.
However, RAID-6 (Erasure Coding) also has some requirements and trade-offs. One of them is that it needs a minimum number of hosts or nodes in the vSAN cluster to function properly. The minimum number depends on the stripe width, which is another rule in the storage policy that defines how many disk stripes are used for each VM object. The stripe width can range from 1 to 12, and the default value is 1.
The formula to calculate the minimum number of nodes for RAID-6 (Erasure Coding) is:
Minimum number of nodes = 2 * stripe width + 2
For example, if the stripe width is 1, then the minimum number of nodes is 2 * 1 + 2 = 4. However, this is not enough for RAID-6 (Erasure Coding), because it can only tolerate one failure with four nodes. Therefore, the minimum number of nodes for RAID-6 (Erasure Coding) with any stripe width is 6. This ensures that there are enough segments and parity information to recover the data from two failures.
Therefore, the correct answer to the question is C. 6. This is the minimum number of VxRail nodes required for a vSAN storage policy with RAID-6 (Erasure Coding).
Reference
- vSAN Erasure Coding – RAID 5 and RAID 6 (vmarena.com)
- Using RAID 5 or RAID 6 Erasure Coding (vmware.com)
- VxRail: what is the FTT and erasure coding ? | Dell Malaysia
- About vSAN Policies (vmware.com)
- Dell EMC VxRail 7.0 vSAN Stretched Cluster Planning Guide (delltechnologies.com)
- vSAN Policies (vmware.com)
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