Thursday, 18 February 2016

What is VMware VSAN 6.2 Erasure Coding?

I have been asked what is the 'Erasure Coding' support in VSAN all about as it gets referenced in the same sentences as the new support for RAID5 and RAID6 configurations (only available in all flash configurations).

VMware is stating Erasure Coding as a term to reference for any data partitioning scheme that allows data to be fragmented but recoverable in case of failure even if some parts  are missing (use of parity). In general reference they are referring to the support of Erasure Coding to represent the fact that they have moved from a mirroring scheme to support both RAID 5 (support for 3+1) and RAID 6 (Support for 4+2) to increase the level of usable data from RAW Capacity across nodes.  

Prior releases only supported a 1+1+witness or worst (1+n where n=failure tolerance but each n was a mirror copy) scheme hence you always needed a minimum 3 nodes to start with but only really got 50% usable capacity at best. This is why the Erasure Code support is getting such big focus as it makes VSAN more efficient with physical resources.

Worth noting that Erasure Coding is not referring to a disk configuration as with RAID but how the fragments are distributed between hosts. It is for this reason that depending on the choice mode also drives the minimum number of hosts required (3 for standard setup, 4 for R5 and 6 for R6).

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