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Erasure Coding in vSAN

Hello and welcome back. We have discussed about compression in vSAN in last few blogs. In this blog, let's discuss about the Erasure Coding in vSAN.


What is Erasure Coding?

Erasure coding is a sophisticated data protection technique employed in vSAN. Unlike traditional methods, it breaks down data into fragments and generates additional pieces known as parity. This distributed approach ensures that even if some components are lost or damaged, the original data can be reconstructed. Essentially, erasure coding enhances data resilience in a vSAN cluster.


Erasure Codes or RAID?

Traditionally, RAID (Redundant Array of Independent Disks) has been the go-to solution for data redundancy. However, vSAN introduces erasure coding as a contemporary alternative. While RAID relies on full copies or mirroring, erasure coding distributes parity across multiple disks, resulting in a more space-efficient storage solution. The trade-off lies in the complexity and computational requirements, making erasure coding an attractive option for modern storage challenges.


Using RAID 5 or RAID 6 Erasure Coding in vSAN Cluster

Choosing between RAID 5 and RAID 6 erasure coding in a vSAN Cluster is vital for data protection and efficient storage use. Both options guard against data loss, offering similar protection to mirroring (RAID 1) but with less storage usage.


With RAID 5 or RAID 6 erasure coding, vSAN can handle the failure of up to two capacity devices in the datastore. RAID 5 is suitable for all-flash clusters with four or more fault domains, while RAID 5 or RAID 6 can be configured for all-flash clusters with six or more fault domains.


Compared to RAID 1 mirroring, RAID 5 or RAID 6 erasure coding requires less additional capacity for data protection. For instance, a VM protected with a Failures to tolerate value of 1 using RAID 1 needs twice the virtual disk size. In contrast, RAID 5 requires only 1.33 times the virtual disk size. The table below provides a general comparison between RAID 1 and RAID 5 or RAID 6.


Image Courtesy - VMware

The above image shows the Capacity Required to Store and Protect Data at Different RAID Levels.


Setting up your virtual machine involves choosing between RAID 5 and RAID 6 erasure coding. For RAID 5, select RAID-5/6 (Erasure Coding) as the Failure tolerance method and set Failures to tolerate to 1. If you prefer RAID 6, use the same Failure tolerance method but set Failures to tolerate to 2. It's important to note that RAID 5 or RAID 6 erasure coding doesn't support a Failures to tolerate value of 3.


Now, if you opt for RAID 1, switch the Failure tolerance method to RAID-1 (Mirroring). RAID 1, known for better performance with fewer I/O operations, can speed up processes like cluster resynchronization compared to RAID 5 or RAID 6.


Space Efficiency vs. Performance

Erasure coding excels in space efficiency, allowing organizations to store data with lower overhead. However, it's essential to recognize the delicate dance between space efficiency and performance. The distributed nature of erasure coding introduces additional computational overhead during data reconstruction, impacting performance compared to simpler storage methods. Striking the right balance involves considering the specific needs of your environment and finding the optimal configuration for your vSAN cluster.


Highlighting Erasure Coding's features and trade-offs in comparison to replication, considering a customer's perspective is key. Erasure Codes offer improved space efficiency compared to Replication for similar data resilience levels. For instance, in a 3+1 RAID-5 setup aiming to tolerate one failure, the space overhead is only 33%, while 2x replication (RAID-1) incurs a 100% overhead. The difference becomes more pronounced with a 4+2 RAID-6 configuration (50% overhead) versus 3x replication (200%) for tolerating up to 2 concurrent failures.

For a more detailed exploration, refer to the insightful blog on The Use of Erasure Coding in vSAN. This resource delves deeper into the intricacies of erasure coding, providing real-world examples and practical insights that complement the foundational understanding provided here.


Erasure coding stands as a cornerstone in vSAN's data protection arsenal. By understanding its principles, comparing it to traditional RAID setups, and navigating the space efficiency versus performance dilemma, you'll be better equipped to optimize your vSAN cluster for both resilience and efficiency. Stay tuned for more insights into the world of vSAN as we unravel its intricacies together.


With this, lets wrap this post here.


Thank you for reading!


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