SupportConsoleDevelopersStart a trialContact

23.6. Partition and File System Tools

This section describes how different partition and file system management tools interact with a device's I/O parameters.

util-linux-ng's libblkid and fdisk

The libblkid library provided with the util-linux-ng package includes a programmatic API to access a device's I/O parameters. libblkid allows applications, especially those that use Direct I/O, to properly size their I/O requests. The fdisk utility from util-linux-ng uses libblkid to determine the I/O parameters of a device for optimal placement of all partitions. The fdisk utility will align all partitions on a 1MB boundary.

parted and libparted

The libparted library from parted also uses the I/O parameters API of libblkid. The Red Hat Enterprise Linux 6 installer (Anaconda) uses libparted, which means that all partitions created by either the installer or parted will be properly aligned. For all partitions created on a device that does not appear to provide I/O parameters, the default alignment will be 1MB.
The heuristics parted uses are as follows:
  • Always use the reported alignment_offset as the offset for the start of the first primary partition.
  • If optimal_io_size is defined (i.e. not 0), align all partitions on an optimal_io_size boundary.
  • If optimal_io_size is undefined (i.e. 0), alignment_offset is 0, and minimum_io_size is a power of 2, use a 1MB default alignment.
    This is the catch-all for "legacy" devices which don't appear to provide I/O hints. As such, by default all partitions will be aligned on a 1MB boundary.

    Note

    Red Hat Enterprise Linux 6 cannot distinguish between devices that don't provide I/O hints and those that do so with alignment_offset=0 and optimal_io_size=0. Such a device might be a single SAS 4K device; as such, at worst 1MB of space is lost at the start of the disk.

File System tools

The different mkfs.filesystem utilities have also been enhanced to consume a device's I/O parameters. These utilities will not allow a file system to be formatted to use a block size smaller than the logical_block_size of the underlying storage device.
Except for mkfs.gfs2, all other mkfs.filesystem utilities also use the I/O hints to layout on-disk data structure and data areas relative to the minimum_io_size and optimal_io_size of the underlying storage device. This allows file systems to be optimally formatted for various RAID (striped) layouts.
Red Hat logoGithubRedditYoutubeTwitter

Learn

Try, buy, & sell

Communities

About Red Hat Documentation

We help Red Hat users innovate and achieve their goals with our products and services with content they can trust.

Making open source more inclusive

Red Hat is committed to replacing problematic language in our code, documentation, and web properties. For more details, see the Red Hat Blog.

About Red Hat

We deliver hardened solutions that make it easier for enterprises to work across platforms and environments, from the core datacenter to the network edge.

© 2024 Red Hat, Inc.