Developers Guide
512 byte and 4K byte sectors
19 Dell EMC SC Series Storage with Oracle ASM | CML1111
C 512 byte and 4K byte sectors
Since consumer-grade HDDs were first introduced in the early 1980s, 512 byte sectors were used. But as
areal density requirements kept increasing on disks, there was a need to increase the sector size. By 2011,
all hard drive manufactures committed to ship new hard drive platforms that supported a new format called
Advanced Format (AF).
Advanced Format uses storage surfaces more efficiently for large files, and allows for the integration of
stronger error correction algorithms to maintain data integrity at higher storage densities. These disks would
be presented to the OS with physical block size of 4K bytes.
Up to a point, Oracle only supported devices presented to the OS with 512 byte physical sectors. With the
advent of the 4K byte physical sectors, Oracle binaries had to change. Depending on the Oracle
configuration, including versions of Oracle software, there are a couple of issues using 4K byte physical
sectors with Oracle and a couple of options available to mitigate the issues. With respect to the 12c
(12.1.0.2.0) environment used for this paper, the only issue discovered pertained to writing spfiles to disk
devices that are presented to the OS with 4K byte physical sectors. This caused issues for the Grid installer
when it tried to create its management repository database, and during the creation of a database using
DBCA.
To mitigate any issue caused by 4K or 512 byte physical sectors with ASMLib, Dell EMC recommends that
the following options be executed in order listed and that Oracle Support is contacted for assistance.
1. If ASMLib is used, it might be possible to configure /etc/sysconfig/oracleasm to direct the ASMLib
driver to use the size of the logical block rather than the size of the physical block. The ASMLib
directive is not supported in all version of Oracle, so check My Oracle Support if it can be used.
ORACLEASM_USE_LOGICAL_BLOCK_SIZE=true
2. Oracle patches are available for download. For a complete list of issues and available patches
pertaining to 4K byte sectors, search for 4K vs 512 byte sectors in My Oracle Support. Some of the
notes will make reference to specific patches that must be applied to the Oracle environment to use
4K byte sectors.
3. Consider using UDEV rather than ASMLib.
4. See the My Oracle Support notes and threads that reference a workaround which makes sure the
storage provider would present the logical and physical block size of volumes that reside on
Advanced Format devices to be 512 bytes. If Oracle Support is unable to resolve issues related to
using 4K byte blocks, contact Dell Copilot for assistance.