System information

determine the I/O parameters of a device for optimal placement of all partitions. The fd i sk utility will
align all partitions on a 1MB boundary.
parted and libparted
The li bparted library from parted also uses the I/O parameters API of l i bbl ki d . The Red Hat
Enterprise Linux 6 installer (An aco n d a) uses l i bparted , 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 al i g nment_o ffset as the offset for the start of the first primary
partition.
If o pti mal _i o _si ze is defined (i.e. not 0 ), align all partitions on an o pti mal _i o _si ze
boundary.
If o pti mal _i o _si ze is undefined (i.e. 0 ), al ig nment_o ffset is 0 , and mi ni mum_i o _si ze
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 al i g nment_o ffset= 0 and o pti mal _i o _si ze= 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 l o g i cal _bl o ck_si ze 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 mi ni mum_i o _si ze and o pti mal _i o _si ze of the
underlying storage device. This allows file systems to be optimally formatted for various RAID
(striped) layouts.
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