Original design of vSAN: devices are arranged in disk groups, each pairing cache with capacity. This differs from ESA's flat storage pool, and VCF accepts either as principal storage.
Also called vSAN Original Storage Architecture.
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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.
- Pairing
Deployment pipelines link an item in one stage to its counterpart in the next. Deploying overwrites a linked item, but an unlinked item that just shares its name gets copied across as a duplicate.
- 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.
- FLAT
A RediSearch vector index that compares every vector exactly, by brute force. It fits smaller data sets or cases needing complete results, whereas HNSW is approximate.
- Storage pool
A group of physical disks collected by Storage Spaces, out of which virtual disks, known as storage spaces, are carved.
- VMware Cloud Foundation
Broadcom's platform for private cloud. It unifies management of NSX, vSAN, vSphere, VCF Automation and VCF Operations as one fleet; VVF, by contrast, lacks automation and cloud management.
- principal storage
Fixed at cluster creation and impossible to switch later: vSAN (ESA or OSA), VMFS over FC, or NFS v3. Supplemental storage, by contrast, can be added afterwards.
Related terms
- Disk group
In the vSAN Original Storage Architecture (OSA), a set made of one flash device for caching and between one and seven devices for capacity, with a maximum of five sets per host. vSAN ESA does away with them, using one storage pool on each host.
- Flash read cache reservation
Only meaningful in hybrid vSAN OSA clusters (ESA and all-flash OSA ignore it), this storage policy rule sets aside read cache on flash for a VM object, sized as a percentage of that object's logical size.
- RAID-5
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.
- Storage pool
The vSAN ESA arrangement in which every claimed NVMe device in a host serves as both cache and capacity in one set, taking the place of OSA disk groups. Unrelated to Windows Storage Spaces pools.
- TRIM/UNMAP
Commands for giving freed space back to storage. ESA turns them on out of the box; OSA and VMFS5 require enabling them or running them by hand, while VMFS6 reclaims automatically.
- vSAN ESA
Newer vSAN design built for NVMe, with one tier and storage pools rather than disk groups. OSA is the older design, using two tiers.
- 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.
- witness appliance
Two-node and stretched vSAN clusters can use this as their witness host. It is an ESX VM that comes ready-built in OVA form, with ESA and OSA each having their own image.