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Creating RAIDZ ZFS Pools With Large ashift/physical-block-size VDEVs May Result In Lower Than Expected Usable Capacity (Doc ID 2017033.1)

Last updated on MAY 10, 2022

Applies to:

Solaris Operating System - Version 10 8/07 U4 and later
F40 Flash Accelerator Card - Version All Versions and later
Flash Accelerator F80 PCIe Card - Version All Versions and later
Sun Flash F20 PCIe Card - Version All Versions and later
Sun Flash F5100 Array - Version All Versions and later
Information in this document applies to any platform.


Newer storage devices, particularly Solid State Disks (SSD), Non-Volatile Memory on PCI (NVME), and Flash Module (FMOD) HBAs, are being released with increasing native physical-block-sizes.  Traditional spinning disks have a physical-block-size of 512 bytes.  SSD, NVME, and FMODS typically have 4K or 8K native block sizes with backwards compatibility to 512e (512 byte emulated).  For optimal performance the native physical-block-size should be used.  This avoids multiple Read-Modify-Write (RMW) operations within the device itself that can lead to premature wear failures and mis-aligned IOs.  Usually this requires the 'physical-block-size' parameter to be added to the driver configuration file.  Refer to the product documentation for the recommended settings.  For example:

For F40 or F80 flash devices, add the following entry to /kernel/drv/sd.conf. In the entry below, ensure that "ATA " is padded to 8 characters. String length of  "ATA     2E256" is 13, and string length of "ATA     3E128" is also 13. Note that this should be a single line in sd.conf. 



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