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.
Also called mirroring.
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Terms in this definition
- 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.
- 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.
- Capacity
A reserved block of compute for a tenant whose size is fixed by its SKU; Fabric F SKUs express it in capacity units (CUs). Workspaces assigned to it unlock features like Copilot, and from F64 upwards people with free licences can view Power BI content.
- Erasure coding
Saves capacity by using parity in place of additional data copies; if a disk fails, the parity is used to rebuild the data. RF2 requires a minimum of four nodes, blocks or racks, and RF3 requires six.
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.
- Number of disk stripes per object
vSAN ESA already uses three stripes for RAID-0 and RAID-1 objects; this storage policy rule sets the minimum number of capacity devices over which each copy of an object is spread, between 1 (default) and 12. More stripes may help performance but consume more resources, and the documentation recommends leaving it at the default.