work with a sector capacity of 4 KB instead of the conventional 512 bytes started about a year ago, but it happened without much ado. Using larger sector capacities has benefits for the hard drive makers in the first place and is typically transparent for the user – but only as long as she or he uses a modern operating system such as Windows 7 or Vista with SP1 and up. Older Windows versions can suffer from performance troubles on 4 KB sector drives, therefore we decided to look at a possible worst case. This article provides an insight, analysis and some recommendations on hard drives with 4 KB sector size – effectively, this applies to the majority of new hard drives available by January 2011.

From 512 Bytes to 4 KB

It took the industry almost a decade between the identification of this change item and the actual implementation of the fix. A sector is the smallest storage unit that can be found on a hard drive and it has been 512 bytes. This made sense in times when hard drives stored megabytes or a few gigabytes, because the sector size represents the minimum amount of capacity that will be consumed even if the file to be stored should be smaller. Hence it made sense to work with a relatively small unit just to avoid wasting capacity and to gain useable space.

However, the 512 byte sector size has turned into a limiting factor. We have to acknowledge that the average file size today is way beyond 512 bytes, which turns the issue of wasted capacity upside down: This is because an Error Correcting Code (ECC) is calculated for each 512 byte chunk, and, as you can imagine, ECC data also requires space to be stored. It goes without saying that one 4,096 byte sector requires less ECC information than eight 512 byte chunks if the ECC algorithms remains unchanged. In the end, the total storage capacity of a hard drive increases as a result of less ECC data overhead.

Increasing Capacity Through 4 KB Sectors

Obviously, the hard drive makers have identified this modification as a powerful step to increase storage capacities. The beauty about this tweak is that it actually makes sense from an architecture standpoint, as other key figures such as x86 memory pages or many file system clusters also have the 4 KB size. In addition, the sector size adjustment represents a soft change and doesn’t require lots of hardware modification as it is the case with an increase in areal density. And, finally, the so-called Advanced Format allows for more robust ECC algorithms, which is important in the light of ever increasing per-drive capacities.

We took two of the latest Toshiba 2.5” SATA hard drives to compare performance between 512 byte and 4 KB sector size and to look at what happens in a worst case, as older system environments may deliver decreased performance on 4 KB sector drives. This would apply to all 4 KB drives, hence the two products we’re using should be considered exemplary.

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