A lot of storage support hardware acceleration, it is able to offload some storage operation from ESXi 5.x host to storage filer, the feature can significantly improve performance during cloning, vMotion, coping…etc.
Different storage device may support different features of hardware acceleration, block device have block zero, full copy, hardware assisted locking, thin provisioning, NAS device have extended stats, file cloning, large scale native SS, native SS to LC, space reserve.
You can find the detail information in this article.
For block storage, we initially create VMFS5 datastore by one LUN, more LUN (extent) maybe added to the datastore when free space is low. Please be sure that all extent of VMFS5 datastore should have same ATS feature, support or not. You may see a error message “Operation failed, unable to add extent to filesystem” when you add a non-ATS extent to ATS enabled VMFS5 datastore.
How to know if lun support ATS?
You can login ESXi 5.x host via SSH and use the command to see supported feature of a lun.
esxcli storage core device vaai status get -d=device id
What is ATS?
Atomic Test and Set (ATS) is new SCSI locking method, it’s try locking per disk sector instead of reserve entire lun. More detail information in this article.