May 21, 201412 yr Given the SATA speeds below: SATA 1.5Gbits/ = 150MB/s SATA 3Gbits/s = 300MB/s SATA 6Gbits/s = 600MB/s Does it really make a difference what you use? The only way to take advantage of the speeds is to use a gigabit connection. If you have a 1 Gigabit NIC/Switch that is still just 128MB/s or less than SATA 1.0 speeds. A 100 megabit switch/router would only be 12.5MB/S 802.11g 54mbits/s = 6.75MB/s I'm seeing on the forum that ~40MB/s seems to be the normal transfer rate. Double that with cache drive. Am I missing something obvious? Like the relationship between the network speed and SATA speed? Can I also assume we are not even going to reach those data rates with 5400-5900RPM HDDs? A 15000 RPM drive would be needed to actually get those rates? Chris
May 21, 201412 yr While SATA is the connection speed to a single drive, the maximum speed, the burst speed, the transfer from disk cache to controller. The SATA speed is not the speed of transfer from media to computer memory. The act of writing to the array is a bit more complicated. In order to complete a write to a parity protected drive, the parity also needs to be written. But before the parity can be written, it has to be calculated. Before parity can be calculated the data for the calc needs to be fetched. So, getting 40MB/sec throughput takes a bit more. Just about all drives will fully utilize the SATA I speed of 1.5Gb. If you have drives connecting at 1.5, you would be wise to correct the problem and likely to see a difference. If all your drives are connected at 3Gb, you should have some headroom for most drives, not SSD perhaps. At SATA III 6Gb, the connection is difficult to saturate with even the fastest spinning disks, indeed getting lots of SATA III ports is rare, typically 2 of the 6 onboard are SATA III. But SATA IV exists because there are devices which will utilize a connection over 6Gb. Like getting your 170MB/s drive on SATA II vs SATA I, if you are using SATA IV devices, you'll want that link. A typical unRAID build will suggest using the two onboard SATA III for cache and parity, data drives on the other four SATA II ports, and populating the slots with enough SATA II ports for your remaining data drives. No need to invest in more SATA III ports at this time. But many reports of performance gains while using SATA II cards, the current drives do easily exceed SATA I.
May 21, 201412 yr Author Thank you for the response. I knew I must have been missing something. Chris
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