The need to conserve space may be a thing of the past for heavy-duty USENET users. Seagate on Monday announced it has shipped over 1 million hard disk drives (HDDs) using shingled magnetic recording (SMR) technology. According to Seagate, SMR technology will play a critical role in developing hard drives of ever-increasing capacity with improved areal density, which is the amount of data that can be stored on a single disk, and is the first step to reaching a 20TB HDD within the next 7 years. A benefit that many USENET users could definetely use!
What is SMR? The process is pretty simple. Track size is traditionally defined by the size of the write heads, as they are larger than the read heads. The track width is larger than necessary from the perspective of reading data back in order to decrease the chances of reading data from adjacent tracks. Seagate’s SMR exploits this reality.
SMR shrinks the guard space between tracks and allows tracks to overlap one another, like roofing shingles. Although data is written to the entire width of the track, a smaller/trimmed portion of the track (the width of the read head) is all that the drive cares about. By allowing tracks to overlap, areal density can continue to scale without further shrinking the size of the heads.
The obvious downside of SMR is actually very NAND flash-like. When writing data sequentially to an empty platter, SMR is full of advantages. When you’re writing to a series of tracks that already contains data, the SMR writing process is actually destructive. Since the writer remains full width and tracks now overlap, overwriting one track will actually harm the next track; those subsequent tracks will need to be overwritten as a result.
Hard drive tracks are typically the size of the write heads, as they are larger than the read heads. However the only part of the track that the read head actually cares about is the central data band; there is guard space the width of the write head either side, which is there to reduce the chance of reading adjacent tracks. SMR takes advantage of this, overlapping tracks to reduce the guard space, allowing areal density to scale without the need for shrinking read/write heads.
As a side benefit, Seagate says SMR technology also improves reliability since it allows the drive maker to use fewer heads and disks to achieve new capacity points.
In 2014 Seagate will move from a 1TB per platter design to 1.25TB per platter thanks to SMR. The increase in platter density will allow Seagate to ship a 4 platter/5TB drive next year. Seagate is hoping to hit higher densities without any performance degradation compared to existing SMR designs. The real question is whether or not Seagate can maintain similar full drive performance compared to a non-SMR drive.
