Home » VMware » 2V0-620 v.2 » Which two statements are true regarding VMware vSphere Flash Read Cache (vFRC)?
Which two statements are true regarding VMware vSphere Flash Read Cache (vFRC)? (Choose two.)
A. Cache fills and cache evictions happen in the granularity of a cache block size.
B. vFRC caches data from both read and write I/Os, but write I/Os are always serviced by the underlying storage.
C. vFRC caches data from both read and write I/Os, but write I/Os are always serviced by the underlying cache data.
D. Cache fills and cache evictions happen in the granularity of the disk block size.
Correct Answer: AB
Explanation/Reference:
Cache fills and cache evictions happen in the granularity of a cache block size. This value ranges from 4KB to 1MB to enable you to best configure your cache block size based on the I/O size of workloads. Even though cache fills and cache evictions happen in the granularity of a cache block size, actual read I/O serviced by the cache can be smaller than the cache block size. For example, if the cache block size is 64KB, and a 4KB read I/O request is issued by the guest virtual machine, and if the data is not available in the cache, a 4KB read is issued to the VMDK. When populating the cache, the vFRC algorithm looks for a 64KB region to place the new 4KB data. If no free space is available, a 64KB region is evicted and the space is used to hold the new 4KB data. The remaining 60KB region in the 64KB cache block is marked as invalid. The cache block size parameter therefore has profound effects on performance
Reference: https://www.vmware.com/files/pdf/techpaper/vfrc-perf-vsphere55.pdf
