Why is there a separate SAS standard when SATA draws inspiration from the same SCSI technology? Additionally, why do SAS/SCSI have higher capacities and speeds than SATA even though SATA 3 doesn't seem to have bandwidth limitations?
When does it really make sense to use SAS, aside from high-load situations, hosting multiple virtual machines, or broadcasting multi-stream videos? And lastly, don't worry about asking "stupid" questions – everyone has to start somewhere!
There are a variety of perspectives on this topic.
From a protocol standpoint, SAS is a highly flexible, reliable, and functional protocol, comparable to ECC technology for memory. Unlike SATA, SAS has two full-duplex ports on devices, making it possible to construct fault-tolerant multi-disk topologies in data storage systems. With end-to-end data protection T.10 and T.10 zoning, SAS can help prevent silent errors caused by data corruption at any level. Additionally, there are different categories of SAS disks, including Enterprise SAS, Nearline SAS, Enterprise SATA, and Desktop SATA, each with unique characteristics that make them better suited for specific applications.
In order to avoid issues down the line, it's important to carefully consider which disk line is best suited for a particular task, taking into account differences in maximum allowable delay, duty cycles, and other factors. The same principles apply to SSD, though there are still many subtleties to navigate in this emerging field.
SAS is not primarily focused on speed and shares many hardware similarities with SATA, differing mainly in firmware. In fact, sometimes SATA can even be faster than SAS if SSDs are used.
However, the main distinguishing feature of SAS currently is its multipath capability. By connecting a disk basket or expander to multiple lines, the load can be distributed and any line failure won't impact system performance. In contrast, SATA lacks this multipath functionality and a line failure can lead to decreased performance or other issues.
SATA was designed to be compatible with SAS, which is essentially a more advanced version of SCSI with all of the enterprise-level features previously discussed. Additionally, there are now 7.2k SAS disks that are mechanically and logically identical to SATA disks but communicate via SAS and are similarly priced.
The biggest difference in market positioning is for enterprise-level applications: SAS disks are used in high-performance systems that are constantly under heavy loads, while large-capacity SATA disks are typically utilized for nearline storage and backups with lower and less frequent usage.
Interestingly, SAS volumes are typically set as multiples of 150GB after reaching a size of 72GB or 146GB to simplify the process of creating RAID arrays using disks from different manufacturers.
In conclusion, the distinctions between the two technologies become clearer at the global market level, with Russia comprising just 6% of this landscape.
Before delving into the potential applications of SAS, it's worth considering the capabilities of NVMe technology. This standard leverages the high performance of flash drives and is capable of delivering much lower latency and higher throughput than SATA or SAS. NVMe drives with a PCI Express interface can be up to 50 times faster than their SATA counterparts and five times faster than those that use SAS. Unlike SATA and SAS, which support only one queue, NVMe allows for more than 65,536 parallel control queues, each with more than 65,536 commands.
However, despite its high performance capabilities, there are still some challenges associated with utilizing NVMe technology in mass storage applications. For example, they are currently more expensive and incompatible with older storage systems. Furthermore, NVMe devices tend to be used in M.2-format devices, limiting the options available for consumers.
On the other hand, SAS was developed with enterprise-level applications in mind. It has several technical advantages over SATA such as the ability to support more than 65,000 devices, thanks to expanders, and higher throughput. The current SAS-4 specification is under development and is expected to leverage a new encoding mechanism and maintain backward compatibility.
The upcoming SAS 24 Gbit/s standard will offer even greater capabilities, doubling bandwidth and offering new features like a 20-bit error correction mechanism and an updated interface connector. This standard will be compatible with 12G SAS and SATA and is designed to provide reliability for enterprise-level applications.
SAS (Serial Attached SCSI) and SATA (Serial ATA) do indeed share some common roots in SCSI technology, but they have evolved to serve different purposes in the realm of storage. SAS was designed with enterprise environments in mind, where reliability, performance, and scalability are paramount. On the other hand, SATA was developed for consumer and small business use, prioritizing cost-effectiveness and ease of use.
One key difference is the target market for each technology. While SATA is aimed at consumer-grade applications and small-scale business environments, SAS is designed to meet the needs of high-performance computing, data center, and enterprise storage solutions. This is reflected in the differences in capacities and speeds. The SAS interface allows for higher capacities and speeds compared to SATA, making it better suited for demanding workloads and mission-critical applications.
Regarding your question about bandwidth limitations, it's important to note that while SATA 3 has a high theoretical bandwidth, it may not always achieve those speeds in real-world scenarios. Additionally, SAS has higher speeds due to its dual-port architecture, which allows for better fault tolerance and multipath capabilities, further enhancing its appeal for enterprise use.
In terms of when it makes sense to use SAS, aside from the high-load situations and use cases you mentioned, SAS is also beneficial in environments where data integrity, reliability, and performance are paramount. This includes scenarios such as high-transaction databases, intensive data analytics, real-time processing, and large-scale virtualization deployments. The dual-port feature of SAS also makes it a preferred choice for mission-critical applications where redundancy and failover capabilities are crucial.
While SATA and SAS share a common ancestry in SCSI technology, they have distinct roles in the storage ecosystem. SATA is well-suited for consumer and small business applications, while SAS excels in enterprise environments that demand high performance, scalability, and reliability. Understanding the specific needs of your storage environment is essential in determining which technology is the most suitable for your requirements.