NETAPP Perfstat Utility Reports Block Misalignment On Zpools with ashift: 12 (Doc ID 1550954.1)

Last updated on AUGUST 10, 2016

Applies to:

Solaris SPARC Operating System - Version 10 10/08 U6 and later
Information in this document applies to any platform.

Symptoms

The NETAPP array side perfstat utility may report "unaligned" IO even while blocksizes used by ZFS are 4KB or a multiple thereof (i.e. zdb -L reports ashift: 12).   E.g., the following analysis from NETAPP is typical for this issue:

 The key indicator here is 100% of IO falls in write_align_histo.6 in the NETAPP proprietary perfstat report.

Changes

For early Solaris 10 and devices not properly supporting the SCSI Logical Blocks Per Physical Block Exponent (LBPPBE), /kernel/drv/ssd.conf can be modified to force the sd physical block size to 4k before we create the zpools, e.g.,

ssd-config-list="NETAPP  LUN", "physical-block-size:4096";

A zpool created after this override is in effect will report "ashift: 12" in zdb -L output.  Reuse of existing NETAPP LUNs of lun-type solaris_efi  in the newly create zpool create this condition.

Cause

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