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Thin provisioning and virtual disks
51 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
12 Thin provisioning and virtual disks
Dell SC Series thin provisioning allows less storage to be consumed for virtual machines, saving upfront
storage costs. This section describes the relationship that this feature has with virtual machine storage.
12.1 Virtual disk formats
In ESXi, VMFS can store virtual disks using one of the four different formats described in the following
sections.
Virtual disk format selection
12.1.1 Thick provision lazy zeroed (zeroedthick)
Only a small amount of disk space is used within the SC Series at virtual disk creation time, and new blocks
are only allocated during write operations. However, before any new data is written to the virtual disk, ESXi
will first zero out the block to ensure the secure integrity of the write. This on-first-write style of block zeroing
before the write induces extra I/O and write latency which could potentially affect applications sensitive to disk
latency or performance.
12.1.2 Thick provision eager zeroed (eagerzeroedthick)
Space required for the virtual disk is fully allocated at creation time. Unlike the zeroedthick format, all the data
blocks within the virtual disk are zeroed out during creation. Disks in this format may take longer to create
than other types of disks because all blocks must be zeroed out before the disks can be used. When using
VAAI, the time it takes to create an eagerzeroedthick disk is greatly reduced. This format is generally used for
Microsoft clusters and the highest-I/O-workload virtual machines because it does not suffer from operational
write penalties like the zeroedthick or thin formats.