vsphere-esxi-vcenter-server-55-storage-guide

Chapter 16 Working with Datastores• Scalability improvements on storage devices that support hardware acceleration. For information, seeChapter 24, “Storage Hardware Acceleration,” on page 235.• Default use of hardware assisted locking, also called atomic test and set (ATS) locking, on storagedevices that support hardware acceleration. For information about how to turn off ATS locking, see“Turn off ATS Locking,” on page 137.• Ability to reclaim physical storage space on thin provisioned storage devices. For information, see“Array Thin Provisioning and VMFS Datastores,” on page 249.• Online upgrade process that upgrades existing datastores without disrupting hosts or virtual machinesthat are currently running. For information, see “Upgrading VMFS Datastores,” on page 142.For information about block size limitations of a VMFS datastore, see the VMware knowledge base article athttp://kb.vmware.com/kb/1003565.VMFS Datastores and Storage Disk FormatsStorage devices that your host supports can use either the master boot record (MBR) format or the GUIDpartition table (GPT) format.With ESXi 5.0 and later, if you create a new VMFS5 datastore, the device is formatted with GPT. The GPTformat enables you to create datastores larger than 2TB and up to 64TB for a single extent.VMFS3 datastores continue to use the MBR format for their storage devices. Consider the following itemswhen you work with VMFS3 datastores:• For VMFS3 datastores, the 2TB limit still applies, even when the storage device has a capacity of morethan 2TB. To be able to use the entire storage space, upgrade a VMFS3 datastore to VMFS5. Conversionof the MBR format to GPT happens only after you expand the datastore to a size larger than 2TB.• When you upgrade a VMFS3 datastore to VMFS5, the datastore uses the MBR format. Conversion toGPT happens only after you expand the datastore to a size larger than 2TB.• When you upgrade a VMFS3 datastore, remove from the storage device any partitions that ESXi doesnot recognize, for example, partitions that use the EXT2 or EXT3 formats. Otherwise, the host cannotformat the device with GPT and the upgrade fails.• You cannot expand a VMFS3 datastore on devices that have the GPT partition format.VMFS Datastores as RepositoriesESXi can format SCSI-based storage devices as VMFS datastores. VMFS datastores primarily serve asrepositories for virtual machines.With VMFS5, you can have up to 256 VMFS datastores per host, with the maximum size of 64TB. Therequired minimum size for a VMFS datastore is 1.3GB, however, the recommended minimum size is 2GB.NOTE Always have only one VMFS datastore for each LUN.You can store multiple virtual machines on the same VMFS datastore. Each virtual machine, encapsulated ina set of files, occupies a separate single directory. For the operating system inside the virtual machine, VMFSpreserves the internal file system semantics, which ensures correct application behavior and data integrityfor applications running in virtual machines.When you run multiple virtual machines, VMFS provides specific locking mechanisms for virtual machinefiles, so that virtual machines can operate safely in a SAN environment where multiple ESXi hosts share thesame VMFS datastore.In addition to virtual machines, the VMFS datastores can store other files, such as virtual machine templatesand ISO images.VMware, Inc. 135