Data Ontap Disk Read Operation; Data Ontap Clearing Space In The System Memory For More Data - IBM N series Hardware Manual

12.3.1 Data ONTAP disk read operation

In Data ONTAP before Flash Cache, when a client or host needed data and it was not in the
system's memory, a disk read resulted. Essentially, the system asked itself if it had the data in
RAM and when the answer was no, it went to the disks to retrieve it. This process is shown in
Figure 12-2.
Figure 12-2 Read request without Flash Cache module installed

12.3.2 Data ONTAP clearing space in the system memory for more data

When more space was needed in memory, Data ONTAP analyzes what it holds and looks for
the lowest-priority data to clear out to make more space. Depending on the workload, this
data might be in system memory for seconds or hours. Either way, it must be cleared, as
shown in Figure 12-3 on page 178.
Chapter 12. Flash Cache
177