USB 3.0 and data storage

USB, as I have written about before, continues to be a popular topic and this seems to be on the increase with the emergence of USB 3.0. The new USB spec yields a number of benefits, but the clearest advantage that it has [over USB 2.0] is potential for higher data transfer speed.

There are a number of applications where the extra throughput can be used to advantage. An obvious example would be multimedia, where HD video needs a lot of bandwidth for faithful renderings. Another application is external disk storage…

As disks [and files] get larger all the time – I observe the 3 TB drives are now quite affordable – speed of data transfer is clearly an issue. USB 3.0 should score here. However, the existing mass storage transport protocol – “bulk only transport” [BOT] – is intrinsically sequential and, hence, cannot take full advantage of SuperSpeed data rates. A new protocol called USB Attached SCSI Protocol [UASP] has been defined. This can make full use of the SuperSpeed bandwidth and is fully compatible with the T10 committee’s SCSI architecture model standard.

The speed of UASP is no better that that delivered by external SATA [eSATA], but it is likely that USB 3.0 will ultimately win out, as all PCs are equipped with USB ports and these will increasingly be USB 3.0. At this time, SuperSpeed enabled external drives do not support UASP, but use BOT, as PC operating systems need to catch up.

My colleague Waqar Humayan, who is a senior engineer with the Mentor Embedded USB team, recently drafted a paper which reviews USB technology in some detail, including an introduction to USB 3.0 This may be downloaded from here.