Why 4K?

George Wilson at ZFS Day

For over 30 years, hard drives have designated the smallest storage location as 512 bytes. In January 2011, all major hard drive manufactures began shipping their hard drive platforms using a new standard called Advanced Format. To aid in the transition, these new hard drives provide a 512 byte emulation mode that allows the drives to advertise themselves as a 512 byte addressable devices. This can severely impact write performance resulting in the need for read-modify-write operations for any misaligned or partial writes that are issued.

The problem is not limited to just physical hardware. Other storage platforms may also provide LUNs (logical unit number) that presents themselves as a 512 byte addressable devices when, in fact, they use a 4K sector size internally. Although ZFS has built-in support for 4K sectors, it has no automatic way of dealing with the lies that the storage devices tell. This talk will focus on the methods that have been developed to work around the lies that hard drive storage platforms tell and will discuss the challenges and drawbacks that come with using 4K sectors.