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Getting Started with VMware Virtual SAN by Cedric Rajendran

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Anatomy of I/O

All the virtual machine data is eventually stored in magnetic disks. The only difference is that some are written immediately and some at a later point in time sequentially.

Let's review specific I/O workflows that are associated with VSAN:

  • Write buffer
  • Data destage
  • Read cache

Write buffer

A guest operating system within the virtual machine performs a write operation intended to the virtual disk associated to the virtual machine. The I/O is received by the Virtual SAN module on the localhost of the virtual machine that it is currently running on. On receipt of the I/O, the VSAN knows the replicas of the virtual disk and triggers a parallel write operation to the replicas. The writes are performed first on the flash devices that frontend ...

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