What Is Near Line SAS?


For many people, Near Line SAS and its difference with the original SAS interface can be confusing. Unfortunately, a lot of information available on the topic on the internet can be too technical and make the difference between a NL-SAS and SAS disk drive too complicated for the typical reader to understand.

This technology, however, can be explained relatively simply, and it can be said that there are several key differences between the two types of disk drive that are of no small importance. It is first of all, however, important to remember that there are three types of interface that are commonly used in today: SAS, NL-SAS and SATA.

The SAS disk drive is now considered the standard for enterprise storage. This is for several reasons, all relating to the advantages that this kind of disk drive brings to its users. Firstly, it is a very robust technology, with its ‘mean time between failure rate’ (MTBF) being 1.6 million hours, which translates into approximately 160 years’ of use.

This can be contrasted with SATA and NL-SAS, where the MTBF rate is around 1.2 million hours. Although this is also very impressive, SAS is still the clear winner when it comes to robustness of the interface for extended use.

SAS is also exceptionally reliable as a technology compared to a SATA or NL-SAS disk drive. When talking about reliability, it is important to consider how many errors occur on the disk’s media platters. In the case of SATA and NL-SAS, the ‘Bit Error Rate’ (BER) is around 1 in every Quadrillion.

This can be contrasted with SAS, which has a BER of 1 read bit error in every 10 Quadrillion. Going by these figures, the latter technology is around 10 times more reliable than the other two, which is quite significant when you take into account that every read error is data lost.

SAS is also superior to SATA and Near Line SAS in that it performs significantly better due to higher RPM speeds of 10k and 15k, compared with the other two’s use of only 7200 RPM. SAS also boasts an impressive average seek time of 3.5 milliseconds, compared with 9.5 milliseconds when it comes to SATA or Near Line SAS.

So what is Near Line SAS and are there any benefits to using this type of disk drive interface? NL-SAS is a newcomer to enterprise storage today, and is a fusion of SATA technology along with SAS interface. This results in an enterprise disk that uses SATA disk platters with SAS connectivity.

Many people benefit from buying a Near Line SAS disk, as they have the option to use it as either SAS or as SATA; if you have both SAS and SATA, NL-SAS is somewhere in the middle of the two. Its reliability and performance, however, are the same as SATA, and not SAS.

In conclusion, it can be said that as Near Line SAS disk drive only has the reliability of SATA, SAS is a more reliable option when you consider both the BER and MTBR rates explained above.Near Line SAS, unfortunately, does not have all the same capabilities of an SAS disk.

On the other hand, SATA will always have better capacity for price, meaning that NL-SAS can be a great cost-effective option that has the added benefits of SAS connectivity at the same time. It should be noted, however, that the SATA and NL-SAS only perform at 7200 RPM, whereas SAS runs at 10k or 15k.

All in all, Near Line SAS does have some benefits, as a blend between SAS and SATA. Despite this, SAS remains the best choice for high level performance, reliability and robustness compared with the other technologies available on the market today.