ONTAP Discussions

Flash Pool - AWA detailed output - Low cacheable reads with high read hit rate




I am trying to analyze Flash Pool candidacy and optimal cache size for an ONTAP cluster. It is running ONTAP 9.3P13. I followed the instructions on this link.


So far so good, been able to interpret most of its output. But then I tried to see the detailed output using the -t option in the print command. It shows information about the volumes in the aggregate that are the best candidates for being on a Flash Pool aggregate.


Happens that for a specific aggregate, the #1 volume in the list is the following:


Volume #1 VOL_XYZ
Summary of the past 7 intervals
Read Throughput (MB/s): 21.545
Write Throughput (MB/s): 12.757
Cacheable Read (%): 0
Cacheable Write (%): 12
Max Projected Cache Size (GiB): 1.856
Projected Read Hit (%): 50
Projected Write Hit (%): 8


So, could someone explain why and how could this volume have 0% of cacheable reads and even so present a Projected Read Hit of 50%?



Pedro Rocha.



Because it is inserted with the writes. If you need specific help,  your SE on your account team can help you review the AWA output as well.


Hello Paul,


I just wanted to understand that output. There are other volumes with apparently strange values. Take a look:


Volume #3 vol_ZXC
Summary of the past 7 intervals
Read Throughput (MB/s): 17.398
Write Throughput (MB/s): 3.266
Cacheable Read (%): 0
Cacheable Write (%): 0
Max Projected Cache Size (GiB): 0.036
Projected Read Hit (%): 12
Projected Write Hit (%): 0


"No cacheable data" but 12% read hit, top 3. How come?


Besides that it would be nice to understand what are the metrics that made up this top 8 rank. Looking at them does not seem to translate the aggregate recommendation.