B3 performance over eSATA

[GodfatherB]

Hi all,

Here is the situation... in my B3 I just changed my original WD Green 2TB with a WD Red 4TB (works very nicely by the way, the temperatures are rougly the same as with Green 2TB), and then I connected the Green 2TB with B3 over eSATA (with a external disk enclosure of course).

Now, I created a manual entry rsync entry in crontab, where I basically ordered a copy of about 1,8TB of data from B3 to external disk. At this very moment it already lasts roughly 24 hours, and it managed to copy roughly 1TB of data - this ammount to about 45.000 files.

I find this performance very poor - when calcualted, this is about 12MB per second. This kind of transfer speed I get over my 100Mbps LAN connection. Over 1 Gbps connection I get speeds (with B3) just around 25MB/s.

Shouldn the speed over the eSATA be limited by disk performance? Honestly, I expected at least 50 MB/s over eSATA, but this not even close to it.

Could there be aproblem with eSATA port on B3?

[johannes]

This is as expected, it's not the eSATA link that is the bottleneck here, but the B3's CPU. You should be able to get the numbers up somewhat by choosing a less CPU intensive transfer method (cp) but I can't say how much difference it will make.

[GodfatherB]

But still... 12MB/s over eSATA from one disk to another, compared to copy from one computer (Windows) to B3 over gigabil link of 25 - 30 MB/s. This still strikes me as too much of a difference?

[Ubi]

what if you push from that windows machine straight onto the esata disk. If you have connection issues, that link should be bad too.

I think the reason why the internal transfer is slow is because it needs the same cpu twice

[GodfatherB]

OK, I tested the copy from Windows machine to eSATA connected disk, and it seems as you suggested, the transfer speed was roughly 25MB7S... so it is true that the cpu just can't handle more than that.

Thanks for the info guys.

[GodfatherB]

Although, now I do wonder what is the point of eSATA, if you can reach the same speeds (due to CPU limitation) over USB. Even if you take 30MB/s as a limit over 1Gbps LAN (again I guess the bottleneck is CPU), this is something USB 2.0 can handle. Why not just 2 additional USB ports instead of eSATA?

[Ubi]

COuld be a marketing decision, but I suppose esata is more robust than a USB when is comes to RAID connections that really do not like hiccups

[johannes]

Ubi is right, esata is considered more stable, RAID over USB is not recommended.