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VMware vSphere offers various VMware Storage APIs for Array Integration (VAAI) that provide the capability to offload specific storage operations to Dell PowerMax. This capability increases both overall system performance and efficiency. One of these supported primitives is Block Zero, which directly impacts eagerzeroedthick disks. Block Zero is also known as “write same” since it uses the WRITE SAME SCSI operation (0x93).
Using software to zero out a virtual disk is a slow and inefficient process. The typical back and forth from host to array is avoided by offloading this task to the array. The full capability of the array can be used to accomplish the zeroing.
When an EZT device is created on VMware with a PowerMax backend, the PowerMax employs block zero to zero out the disk. As explained, most arrays then reserve that space equal to the VMDK size; however, the PowerMax architecture is different and no space is reserved. The PowerMax can be thought of as a single pool of storage, since new extents can be allocated from any thin pool on the array. Therefore, the only way that a thin device can run out of space is if the entire array runs out of space. It was deemed unnecessary to reserve space on the PowerMax when using block zero. Even so, the array changes the extents to prime them for data. The array must still process the write same requests from VMware. So, the creation time for an EZT VMDK is not as quick as the other formats.
Block Zero is enabled by default and does not require any user intervention. If wanted, Block zero can be disabled on an ESXi host by using the vSphere Client or command-line utilities. Block zero can be disabled or enabled by altering the setting DataMover.HardwareAcceleratedInit in the ESXi host advanced settings under DataMover.
NVMe over fabrics, or NVMeoF, defines a common storage architecture for accessing the NVMe block storage protocol over a storage network. This means going from server to SAN, including a front-end interface to NVMe storage. There are any number of fabrics that make up NVMeoF including FC, RoCE, and IP. Dell offers two implementations of NVMeoF - FC and IP - or FC-NVMe and NVMe/TCP. NVMeoF devices do not use the VAAI Plugin, however some of the VAAI SCSI commands have been ported over. WRITE SAME or Block Zero is implemented as the command Write Zeroes on NVMeoF and deallocate is used for UNMAP. These commands provide the same functionality as the SCSI command. XCOPY is not yet ported.