LSI Logic Parallel: This was formally known as LSI Logic and was the other SCSI virtual controller available originally in VMware ESX, used for operating systems such as Windows Server 2003.It does not support VMDK larger than 2 TB. Now it's a legacy controller used mainly for legacy operating systems. BusLogic: This is one of the first emulated SCSI virtual controllers available in VMware ESX.There are different types of controller available for a VM running on ESXi which are described as follows: To access a block device, such as virtual disks VMDK, virtual CD/DVD-ROM, or other SCSI devices, each VM uses storage controllers at least one is added by default when you create a VM. For random I/O, thin VMDKs have the worst performance and higher latency (for lazy thick, it depends if you have to write a new block). There is no significant difference in performance for sequential I/O between the different types of virtual disks. Except for building guest clusters (clusters across VMs on different hosts), there is no need to use these types of disk. There are also Raw Device Mapping ( RDM) disks where a disk at ESXi level is mapped 1:1 to a VM (like a Passthrough mode), with two different types of compatibility (virtual or physical mode). Note that you can also change the type of each individual disk, by choosing Configure per disk on the new HTML5 client shown as follows: You can choose the disk provisioning type during virtual disk creation, but you can change the type using a cold VM migration across two datastores, or using Storage vMotion (if you have at least ESXi Standard edition). Unused space is available for use by other VMs. Thin VMDK: Space required for the thin-provisioned virtual disk is allocated and zeroed on demand as space is used.The entire disk space is reserved and unavailable for use by other VMs. Before writing to a new block, a zero has to be written, increasing the input/output operation per second ( IOPS) on new blocks compared to eager disks. This space may contain stale data on the physical media. Thick or lazy zeroed thick VMDK: A thick disk has all space allocated at creation time.Such disks may take a long time during creation compared to other disk formats. An eager zeroed thick disk has all space allocated and wiped clean of any previous content on the physical media at creation time.The type of virtual disks are mainly the same since vSphere 4.0: There are different types of virtual disks depending on the provisioning method, pre- allocated or dynamic. But note that USB datastores are just unsupported by VMware.
VMware vSphere supports different types of storage architectures, both internally (in this case the controller is crucial, that must be in the HCL) or externally with shared SAS DAS, SAN FC, SAN iSCSI, SAN FCoE, or NFS NAS (in those case the HCL is fundamental for the external storage, the fabric elements, and the host adapters).įor local storage, with vSphere 6.x it's possible to use USB disks, not only as boot disks, but also to run VMs.
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