Docking station - eSATA port to drive connection

[0weQ]

Hi All,

The question asked below addresses as following, a hard disk docking station by 3rd-party vendor. Station take 2.5 and 3.5 inch drives, hdd and ssd. Towards the host it offers USB 3.0 and eSATA interfaces. Towards the housed drive it support SATA interface up to 6GB or SSD x 1.

The vendor specifies the eSATA port speed to 3GB. However, I guess between the eSATA port and the drive plugged in there is not translation nor an adapter unit necessary. eSATA port pings could connect 1:1 to SATA drive interface. My local retailer has confirmed this assumption. Where does the lowering of the interface speed from 6GB to 3GB come from?

Vast majority of docking stations with eSATA port and compatible with SATA III drives and availble in sale are specified to 3GB regarding the eSATA port speed.

* Can it be that depending on the station model and/or vendor there is some translation or adaption unit within the chain eSATA port to housed SATA III drive and a cut-down of interface speed results from this?
* Can it be that the eSATA port specification of 3GB in product description is not correct?

 

[mbarnes86]

Hi

My guess because there is USB 3.0 OR eSATA in to the docking station and SATA to hard disk controller,
the USB 3.0 to SATA bridge chip can not achive SATA 6 GB (III) speed

In practice this is only important with SSD

If there was no USB 2.0 or 3.0 input then the eSATA / SATA would run at speed of motherboard SATA controller without going through any chip or interface

regards
Mike Barnes

 

[0weQ]

> ...the USB 3.0 to SATA bridge chip can not achive SATA 6 GB (III) speed
Sure, although USB 3.0 can, with all overheads included, achieve 5GB.

So you think if the dock shows also USB (2.0 or 3.0) - it looks this way in case of this dock indeed -
the bridge will also pass-through SATA connection, from eSATA port to internal SATA slot. Is it so?
I do not undertand why does the SATA connection (eSATA port to SATA internal slot) be routed through
the USB bridge.

> In practice this is only important with SSD
What is the reason of be important with SSD? This is interesting point. This dock is receives today only HDD.
But who knows how soon will I need to use also SSD with this dock. Therefore it will be good to know
how the eSATA port to SATA internal slot connection will look and work.

Actually all these questions arose because I am on ordering such a dock.
It should provide its services for the time as long as possible. Means its perfomance
must be suitable for long term usage.
Is the conclusion from whole discussion I will be on the good side if eSATA-port capable hard disk dock station
whose eSATA port is specified to 6GB speed will be ordered?

 

[Paperdoc]

You are right to suggest that an eSATA connection need not involve the USB3 bridge chip. It can be almost a straight-through connection. However, there has to be a LITTLE bit of circuitry involved to establish which interface is in use. I do know that, on my older eSATA enclosure containing a SATA II (now called SATA 3 Gb/s) HDD, its data transfer speed is virtually the same as identical drives mounted internally.

The ACTUAL data transfer rate using the most modern SATA HDD units in any connection system comes somewhere in the 150 to 200 MB/s range. That is just over the ORIGINAL SATA 1.5 Gb/s data rate, and not even close to the limit of the 3 Gb/s rate. So why the fast rate specs? Those are the specs for the maximum data communication rate of the COMMUNICATION SYSTEM between the HDD unit and the controller chip. But in fact the real limit on average data transfer rate for any mechanical HDD (that is, one with spinning disks and moving heads) is imposed by those moving mechanical components. Having the COMMUNICATION system capable of faster data transfer merely means that the comm system will NOT limit the HDD's performance. And having an even faster SATA 6 Gb/s comm system actually does NOTHING to speed up mechanical HDD's. So, whether the interface between the computer and the dock can communicate at 3 or 6 Gb/s makes no difference at all for mechanical units.

The disk manufacturer is correct is specifying that, at the interface from dock to HDD it conforms to 6Gb/s specs. Any SATA 6Gb/s device will negotiate with its communication partner and set an actual data transfer max speed according to their mutual capabilities. So a SATA 6Gb/s HDD WILL perform just fine on an eSATA link operating at 3 Gb/s. Moreover, if the drive plugged into the dock is a mechanical HDD, there will be NO effect on the actual data transfer rate.

Now, when you get to SSD's the answers change a bit. Early ones also rarely exceeded 3 Gb/s actual data transfer rates, although they certainly were faster than HDD's. The most recent SSD's, however, can exceed 3 Gb/s performance, but not get too close to the 6 Gb/s rate. So, the design of USB3 and of the 6 Gb/s communication system for SATA devices has succeeded - the communication system is still NOT limiting the performance of even the fastest SATA devices, SSD's. It IS true that an eSATA system that operates at 3 Gb/s MAY slow down an SSD's performance plugged into that dock, but not by a lot.

On the other hand, there are eSATA controller systems now that operate also at 6 Gb/s comm rates. So, IF your computer has such an eSATA system, it would be interesting to know whether the dock has any components that slow that speed down, or does the dock operate at the host's eSATA speed, whatever that is?