Dave's PCF WIP: Terms

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read scan operation

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"Read scan operation" refers to a maintenance operation performed to identify and mitigate or avoid or counter errors in the data or storage cells and/or other components of a non-volatile storage device. A read scan operation may be referred to, interchangeably, as a "read scan" or “read scan operation.” In one embodiment, a read scan operation involves reading data from, or sensing a determinable physical characteristic, or a memory state of storage cells in a storage block. Next, the read scan operation checks the memory states of the storage cells for any errors, corrects as many errors as possible, and determines a bit error rate. Then, the read scan operation determines if the bit error rate satisfies a threshold such as a read bit error rate threshold.In one embodiment, the read scan operation reads data from each logical page, or word line, of the storage block. In another embodiment, the read scan operation selects less than all of the logical pages of the storage block. In other words, the read scan operation may sample the logical pages of the storage block from which to read data for the read scan operation.If a read bit error rate threshold is satisfied, the read scan operation then may perform a data scrub operation or a data refresh operation. In certain embodiments, a read scan operation may always include a data scrub operation or a data refresh operation. In other embodiments, performing a data scrub operation or data refresh operation may be conditioned on the bit error rate satisfying a read bit error rate threshold. In such embodiments, a read scan operation may be referred to as a “read scrub” or "read scrub operation." In these embodiments, a read scan operation may conditionally include a data scrub operation.In certain embodiments, a read scan operation may operate as a foreground process meaning that the read scan operation interrupts, or delays, a non-volatile storage device from servicing read commands or write commands for a host. In addition, the read scan operation may need to complete working on a particular storage block and thereby delay a host read command for data on that particular storage block. Thus, in such embodiments, a read scan operation may impact quality of service levels between a host and the non-volatile storage device.