[CentOS] SAS/SATA DAS

[John R Pierce]

> 
> >Sorry for hi-jacking this thread, but it's very interesting. What's the difference, apart from the speed & price between SAS & SATAII?
> 
> SAS is more enterprise geared, relating to speed and MTBU (probably a load of crap on that point)
> and SATA is cheaper and does not perform as well, supposedly less reliable to.
> 
> SAS usually only come in higher spindle speeds and the 2.5" variety actually only have 300 Gb ratings.


SAS supports proper multiplexor technology, and multichannel bonding... a typical external SAS connector has FOUR sas channels, and the multiplexor in a drive chassis can connect any drive to any channel at any time, while SATA only supports simple expanders (1 channel to N drives).  SAS understands NCQ natively, while this was a kludge added to SATA (and, from various field reports, not very well).