Linux Not Fully Prepared for 4096-Byte Sector Hard Drives
Feb 16, 2010, 14:33 (1 Talkback[s])
"Recently, I bought a pair of those new Western Digital Caviar
Green drives. These new drives represent a transitional point from
512-byte sectors to 4096-byte sectors. A number of articles have
been published recently about this, explaining the benefits and
some of the challenges that we'll be facing during this transition.
Reportedly, Linux should unaffected by some of the pitfalls of this
transition, but my own experimentation has shown that Linux is just
as vulnerable to the potential performance impact as Windows XP.
Despite this issue being known about for a long time, basic Linux
tools for partitioning and formatting drives have not caught
up.
"The problem most likely to hit you with one of these drives is
very slow write performance. This is caused by improper
logical-to-physical sector alignment. OS's like Linux use 4K blocks
(or multiples of 4K) to store data, which matches well with the
physical sector. However, nothing restricts you from creating a
partition that starts on an odd-numbered 512-byte logical sector.
This misalignment causes a performance hit since the drive has to
read and rewrite the 4K sectors with whatever 512-byte slices
changed.
"WD claims to have done some studies and found that Windows XP
was hardest hit. By default, the first primary partition starts on
LBA block 63, which obviously is not a multiple of 8. They provide
a utility to shift partitions by 512 bytes to line them up. WD also
tested other OS's and declared both MacOS X and Linux to be
"unaffected". I don't know about MacOS, but with regard to Linux,
they are not entirely correct. Following are the results of my
experimentation."
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