When to Add the First Read Cache Device (BUI)

Use the following procedure to determine if you need a first read cache device for the appliance. To determine if you need more than one device, see When to Add More Read Cache Devices (BUI).

1. Create a worksheet as described in Creating a Worksheet (BUI).
2. Click the add icon next to Add statistic.
3. Go to CACHE > ARC accesses > Broken down by hit/miss.
4. Click metadata hits under the Range average column to show the graph of ARC accesses per second, broken down by hit/miss.
5. Click the drilldown icon and select By L2ARC eligibility.
6. Click data hits to show the graph of ARC accesses per second, broken down by hit/miss.
7. Click the drilldown icon and select By L2ARC eligibility.
8. Wait several minutes.

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   Note -  This wait time can be adjusted to better determine your peak I/O. Capturing analytics for 24 hours during normal business operations may reveal the best understanding of your IO patterns.

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9. Examine the graphs.

   Consider adding the first read cache device when all of the following conditions are present:

   • There are at least 1500 L2ARC-eligible ARC access misses for data and/or metadata per second

   • The appliance has an active filesystem or LUN with a ZFS record size of 32k or smaller