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SATA 3 hard disk can be connected to SAS ports. But If i connect SATA 3 drive to a SAS port then can i get same speed as SATA 3 originally offers or will it be a difference? Will it reduce the performance than connecting to a SATA 3 port.

I have a intel server board which has more number of SAS ports and i have to connect my SATA 3 drives to these SAS ports.So i am concerned about the performance. So please help me on this

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The first thing that should be noted is that for most practical workloads of a single mechanical disk, even SATA1 which offers a transfer rate of 150 MB/s would not present a bottleneck. The higher transfer rates are mainly relevant for either cached I/O or high-performance SSDs. The first case is rare enough not to make a significant difference in overall performance. The latter case is only a concern if your SSD actually is performing better than the link can handle even over a long term (SSD performance typically degrades as the disk fills up). So unless you are building a corner-case setup, you would not notice a performance difference, no matter the link speed.

Now the technical part: there are two SAS standards - the older SAS 1 with a data rate of 3 Gbps and the newer SAS2 with a data rate of 6 Gbps per link. Both include SATA compatibility. SAS1 controllers would negotiate SATA2 speeds (300 MB/s) with connected SATA devices. Most newer SAS2 controllers will negotiate SATA3 speeds (600 MB/s) with capable devices. You should simply consult your controller's documentation / spec sheet to see what it would support.

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