Something that I only just recently noticed is that we have made a change to the sub-blocks structure on VMFS-6, compared to VMFS-5. Sub-blocks are small allocations on a VMFS volume, and they are used to back small files. They were introduced as a space-saving measure to prevent using a full file block to back a very small file. To put this simply, when a file is created on VMFS, it is initially backed by a sub-block, and when the file grows above the size of a sub-block, it is switched to being backed by a file block (this has…
When vSphere 6.5 released towards the end of 2016, it introduced a brand new version of VMFS, VMFS-6. VMFS probably needs little in the way of introduction at this stage, it being VMware’s flagship filesystem for over 10 years at this point. There is an older VMFS whitepaper available here if you are new to VMFS and want to get more of an overview. Now VMFS-6 introduces two new internal block sizes concept for file creation. These are referred to as LFB (Large File Blocks) and SFB (Small File Blocks) and are used to back files on the VMFS-6 volume.…