Single-parity erasure coding in vSAN, surviving one failure more economically than mirroring. ESA switches adaptively between 2+1 and 4+1, whereas OSA uses 3+1 and so needs four fault domains.
Also called erasure coding, single parity.
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Terms in this definition
- vSAN
VMware's software-defined storage, which combines local devices across a cluster's ESX hosts into one shared datastore. Available as OSA or ESA, VCF can use it as principal storage.
- Mirroring
A way of keeping a copy of an outside database, for example Azure SQL Database, Cosmos DB or Snowflake, continuously up to date in OneLake as Delta tables inside a mirrored database. You query it in T-SQL via its SQL analytics endpoint, and the replication compute costs nothing.
Related terms
- FTT
Failures to tolerate: how many disks or hosts can fail without losing a VM object, met by mirroring (RAID-1) or erasure coding (RAID-5/6). vSAN's default policy uses one.
- RAID-1
Mirroring in vSAN: whole duplicate copies of an object sit on separate hosts. It handles between one and three failures, at a higher capacity cost than erasure coding.
- RAID-6
Double-parity erasure coding in vSAN: data is spread 4+2 across at least six fault domains, so two simultaneous failures can be survived.
- vSAN space efficiency
Features that cut how much raw capacity vSAN needs, including compression, deduplication, TRIM/UNMAP and RAID-5/6 erasure coding. What is available varies between OSA and ESA.