When to Add More Read Cache Devices (CLI)

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Use the following procedure to determine if you need more read cache devices for the appliance.

Before You Begin

Go to maintenance hardware show to identify which chassis and slots contain read cache devices.

Create a worksheet as described in Creating a Worksheet (CLI), select that worksheet, and then enter dataset.
```
hostname:analytics worksheets> select worksheet-000
hostname:analytics worksheet-000> dataset
```

Add a read cache device to the worksheet, broken down by percent utilization, and then enter commit. Repeat for each read cache device used by the appliance.

hostname:analytics worksheet-000 dataset (uncommitted)> set name="io.utilization[disk=hostname/HDD 13]"
                           name = io.utilization[disk=hostname/HDD 13]
hostname:analytics worksheet-000 dataset (uncommitted)> commit

Enter done, and then enter done again to exit the context.

hostname:analytics worksheet-000> done
hostname:analytics worksheets> done

Wait at least 10 minutes, and then go to analytics datasets.
```
hostname:> analytics datasets
```

Enter show to view a list of available datasets.

hostname:analytics datasets> show
Datasets:

DATASET     STATE    INCORE  ONDISK  NAME
dataset-000 active    1.27M   15.5M  arc.accesses[hit/miss]
dataset-001 active     517K   9.21M  arc.accesses[hit/miss=metadata hits][L2ARC eligibility]
...
dataset-021 active     290K   7.80M  io.utilization[disk=hostname/HDD 13]
hostname:analytics datasets>

Enter select and the first dataset that you added.
In this example, dataset name io.utilization[disk=hostname/HDD 13] corresponds to dataset-021.
```
hostname:analytics datasets> select dataset-021
```
Enter read 600 to read the last 600 seconds, or 10 minutes, of the dataset.
```
hostname:analytics dataset-021> read 600
```
Repeat steps 6 and 7 for each dataset that you added to the worksheet.
Examine the data.
You may want to add more read cache devices when existing devices are 90% utilized.