AK
ReFS cluster sizes
ReFS offers both 4K and 64K clusters. 4K is the default cluster size for ReFS, and we recommend using 4K cluster sizes for most ReFS deployments because it helps reduce costly IO amplification:
In general, if the cluster size exceeds the size of the IO, certain workflows can trigger unintended IOs to occur. Consider the following scenarios where a ReFS volume is formatted with 64K clusters:
Consider a tiered volume . If a 4K write is made to a range currently in the capacity tier, ReFS must read the entire cluster from the capacity tier into the performance tier before making the write . Because the cluster size is the smallest granularity that the file system can use, ReFS must read the entire cluster, which includes an unmodified 60K region, to be able to complete the 4K write.
If a cluster is shared by multiple regions after a block cloning operation occurs, ReFS must copy the entire cluster to maintain isolation between the two regions. So if a 4K write is made to this shared cluster, ReFS must copy the unmodified 60K cluster before making the write.
By choosing 4K clusters instead of 64K clusters, one can reduce the number of IOs that occur that are smaller than the cluster size, preventing costly IO amplifications from occurring as frequently.
ReFS offers both 4K and 64K clusters. 4K is the default cluster size for ReFS, and we recommend using 4K cluster sizes for most ReFS deployments because it helps reduce costly IO amplification:
In general, if the cluster size exceeds the size of the IO, certain workflows can trigger unintended IOs to occur. Consider the following scenarios where a ReFS volume is formatted with 64K clusters:
Consider a tiered volume . If a 4K write is made to a range currently in the capacity tier, ReFS must read the entire cluster from the capacity tier into the performance tier before making the write . Because the cluster size is the smallest granularity that the file system can use, ReFS must read the entire cluster, which includes an unmodified 60K region, to be able to complete the 4K write.
If a cluster is shared by multiple regions after a block cloning operation occurs, ReFS must copy the entire cluster to maintain isolation between the two regions. So if a 4K write is made to this shared cluster, ReFS must copy the unmodified 60K cluster before making the write.
By choosing 4K clusters instead of 64K clusters, one can reduce the number of IOs that occur that are smaller than the cluster size, preventing costly IO amplifications from occurring as frequently.