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4K-sector drives and Linux

Mar 19, 2010, 18:04 (0 Talkback[s])
(Other stories by Jonathan Corbet)

"Almost exactly one year ago, LWN examined the problem of 4K-sector drives and the reasons for their existence. In short, going to 4KB physical sectors allows drive manufacturers to increase storage density, always welcome in that competitive market. Recently, there have been a number of reports that Linux is not ready to work with these drives; kernel developer Tejun Heo even posted an extensive, worth-reading summary stating that "4 KiB logical sector support is broken in both the kernel and partitioners." As the subsequent discussion revealed, though, the truth of the matter is that we're not quite that badly prepared.

"Linux is fully prepared for a change in the size of physical sectors on a storage device, and has been for a long time. The block layer was written with an avoidance of hardwired sector sizes in mind. Sector counts and offsets are indeed managed as 512-byte units at that level of the kernel, but the block layer is careful to perform all I/O in units of the correct size. So, one would hope, everything would Just Work.

"But, as Tejun's document notes, "unfortunately, there are complications." These complications result from the fact that the rest of the world is not prepared to deal with anything other than 512-byte sectors, starting with the BIOS found on almost all systems. In fact, a BIOS which can boot from a 4K-sector drive is an exceedingly rare item - if, indeed, it exists at all. Fixing the BIOS is evidently harder than one might think, and, evidently, there is little motivation to do so. Martin Petersen, who has done much of the work around supporting these drives in Linux, noted:"

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