Which cache management algorithm occurs continuously, at a modest rate, when the cache
utilization level is between the high and low watermark?

A.
Forced flushing

B.
Idle flushing

C.
Vault flushing

D.
High watermark flushing

Explanation:
Cache Management: Watermarking
As cache fills, the storage system must take action to flush dirty pages (data written into the cache
but not yet written to the disk) to manage space availability. Flushing is the process that commits
data from cache to the disk. On the basis of the I/O access rate and pattern, high and low levels
called watermarks are set in cache to manage the flushing process. High watermark (HWM) is the
cache utilization level at which the storage system starts high-speed flushing of cache data. Low
watermark (LWM) is the point at which the storage system stops flushing data to the disks. The
cache utilization level drives the mode of flushing to be used:
• Idle flushing: Occurs continuously, at a modest rate, when the cache utilization level is between
the high and low watermark.
• High watermark flushing: Activated when cache utilization hits the high watermark. The storage
system dedicates some additional resources for flushing. This type of flushing has some impact on
I/O processing.
• Forced flushing: Occurs in the event of a large I/O burst when cache reaches 100 percent of its
capacity, which significantly affects the I/O response time. In forced flushing, system flushes the
cache on priority by allocating more resources.
EMC E10-001 Student Resource Guide. Module 4: Intelligent Storage System