Database Reference
In-Depth Information
Caution
For the vast majority of environments, you don't need to change the default VMFS
settings, and the information in this section should be considered carefully
alongside your knowledge and understanding of your particular environment,
circumstances, and requirements. This really is for when you're considering
virtualizing business-critical apps and Monster VMs with very large storage
footprints.
In vSphere 5.5, the whole VMFS Heap size problem has been addressed. The VMFS
Heap is now irrelevant as a measure of how much open and active VMDK capacity a
single ESXi 5.5 host can handle. This is due to major improvements in the way the
VMFS Heap and pointer blocks are managed.
VMFS pointer blocks are a pointer to a VMFS block on disk. When a VMDK is opened
on an ESXi 5.5 host, all of the VMFS “pointer” blocks are cached in the Pointer Block
Cache, which is not part of the main VMFS Heap (where the pointer blocks were
previously stored in prior versions of ESXi). This allows the open VMFS “pointer”
blocks to be addressed or accessed and managed as fast as possible without having to
access metadata from the VMFS file system directly. The pointer blocks will remain in
use so long as a VMDK or other file is open. However, many blocks in any individual
VMDK are not often active. It's usually only a percentage of the blocks that are actively
used (say, 20%). The images shown in
Figures 6.21
and
6.22
display how the pointer
blocks are used to refer to data blocks on the VMFS file system. Each pointer block that
is active is stored in the pointer block cache to ensure the fastest possible access to the
most frequently used blocks.
