A hardware-assisted locking primitive for block storage that locks a VMFS disk sector by sector, avoiding SCSI reservations on the entire device.
Also called Atomic Test and Set.
Read more: Broadcom TechDocs
In the Ultra Transcenders books
Each book explains ATS in context, with comparison tables and the common traps.
Terms in this definition
- General-purpose v1
The older storage account kind (
Storage), which lacks access tiers, Archive and premium file shares and retires on 13 October 2026. Converting to ZRS requires first upgrading to GPv2, a one-way change. - VMFS
Clustered file system for block datastores, whether the storage is iSCSI, local or FC-attached. Unlike VMFS5, VMFS6 can use 4Kn devices and reclaims freed space by itself.
- SCSI
Small Computer System Interface, a standard for connecting disks. Hyper-V lets you hot-add or remove virtual SCSI disks on a running VM, and generation 2 VMs start up from them.
Related terms
- ATS-only
A VMFS locking mode relying solely on ATS, used by VMFS5 and VMFS6 datastores newly formatted on capable storage. These datastores cannot extend across devices lacking ATS.
- ATS+SCSI
Locking mode for VMFS with a fallback: it starts with ATS, then uses SCSI reservations, holding an entire device while metadata changes. Seen on VMFS5 upgraded from VMFS3, and on new datastores where devices lack ATS.
- Block primitives
Storage tasks that a block array performs in place of ESX, namely XCOPY for copying, write same for zeroing and ATS for locking.