512e and 4Kn Disk Formats This paper provides the context for 512e and 4Kn disk format migration, as well as pointing out the long-term benefits to customers and potential pitfalls to avoid when moving from 512-byte to 4K sector formats.
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Contents 1 Overview ......................................................................................................................................................................................... 4 2 Background .....................................................................................................................................................................................5 3 The long-term benefit of 4K sectors .................................................................
1 Overview A change is coming in the hard drive industry. As storage densities dramatically increase, one of the most elemental aspects of hard drive design — the logical block format size known as a sector — has remained constant. The storage industry is quickly ramping up efforts to transition to a new type of format for media, known as Advanced Format, which has a 4KB physical sector size.
2 Background The legacy sector format contains a Gap section, a Sync section, an Address Mark section, a Data section and Error Correction Code (ECC) section as shown in Figure 1. Figure 1 Legacy sector format The sector layout is structured as follows: • Gap"section:"The"gap"separates"sectors. • Sync"section:"The"sync"mark"indicates"the"beginning"of"the"sector"and"provides"timing"alignment. • Address"Mark"section:"The"address"mark"contains"data"to"identify"the"sector’s"number"and"location.
3 The long-term benefit of 4K sectors Since all hard drive manufacturers have agreed to transition to the Advanced Format sector, the industry must adapt to and embrace this change to minimize potential negative side effects. Short-term benefits to end users will not be dramatic in terms of immediate capacity increases. However, the migration to 4Ksized sectors will most definitely provide quicker paths to higher areal densities and hard drive capacities, as well as more robust error correction.
4.1.1 Emulated read and write processes To read data from a 4K sector formatted drive in 512 emulation mode, the process is very straightforward, as shown in Figure 7. Figure 2 Potential read sequence for 512-byte emulation The process of reading the 4K block of data and reformatting to the specific 512-byte emulated sector requested by the host computer is performed in the drive’s DRAM memory and does not measurably impact performance.
4.1.2 Aligned versus unaligned hard drive partitions Up to now we have not discussed how host systems and hard drives communicate the location of sectors on the media. It’s time to introduce the Logical Block Address (LBA). Each 512-byte sector is assigned a unique LBA, from zero (0) to the number required based on the size of the disk. The host requests a specific block of data using the assigned LBA.
4.3 Mixing drives If you decide to use a mix of drive types, but do not resolve these issues, the overall storage performance may be lower than expected. To mix drives, you must have a good understanding of the operating system, applications, and the configuration such as RAID, volumes, and so on. To ensure compatible drive mix, check with your Dell team.
There are a number of software utilities (such as Diskpart and Paragon) that are widely used by system builders, OEMs, value-added resellers, and IT managers for aligning partitions when the operating system doesn't offer or support partition alignment out of the box. Systems today typically consist of multiple hard drive partitions. This means that each partition on the hard drive must be created with 4K-aware partitioning software to make sure proper alignment and performance is ensured. 5.
5.5 Dealing with unaligned conditions Using a 4K-aware version of an operating system to create hard drive partitions is a simple, straightforward method for avoiding unaligned conditions. Some third-party firms offer utilities that examine existing hard drive partitions and realign them as needed. This alternative takes additional time and adds steps to the system building or upgrading process.
7 Figure 5 Advanced Format emulation logos Figure 6 Advanced Format native logos Conclusion The industry transition away from the legacy 512-byte sector is a certainty, and gives hard drive suppliers another tool for driving improved areal densities. Dell and our customers both benefit from this transition through higher capacity hard drives and continued reliability. The key to a smooth transition is a well-educated storage community who can avoid potential performance pitfalls.
