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ZFS ARC can shrink down without memory pressure result in slow performance (Doc ID 1404581.1)

Last updated on MARCH 11, 2021

Applies to:

Solaris x64/x86 Operating System - Version 10 10/08 U6 to 11.1 [Release 10.0 to 11.0]
Solaris Operating System - Version 11 to 11.1 [Release 11.0]
Information in this document applies to any platform.

Symptoms

The ZFS ARC (Adaptive Replacement Cache) is used for caching file system blocks. It has been noticed that the ARC can shrink too low without any sign of memory pressure and remain there on Solaris 11.

When this happens, L2ARC (if configured) is not fed any more data. That may cause slow application performance.

This issue can happen after ARC size increases to it's maximum limit (3/4 of physical memory by default). It then continues to drop too low and the flag arc_no_grow is set to TRUE and not changed back to FALSE.

You can check the size of ARC and  this flag by running:

Cause

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In this Document
Symptoms
Cause
Solution


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