Re: how do export a block device via eSATA?

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At Sun, 13 Feb 2011 21:58:11 +0200 CentOS mailing list <centos@xxxxxxxxxx> wrote:

> 
> On Sun, Feb 13, 2011 at 9:44 PM, Robert Heller <heller@xxxxxxxxxxxx> wrote:
> > At Sun, 13 Feb 2011 11:00:39 -0800 CentOS mailing list <centos@xxxxxxxxxx> wrote:
> >
> >>
> >> On 02/13/11 10:53 AM, Rudi Ahlers wrote:
> >> > Does any one know how to, if at all possible currently, to export a
> >> > block device via eSATA? i.e. how do I do something like iSCSI, but
> >> > over eSATA?
> >> >
> >> > I have a cheat ($15 probably?)  media player at home (Egreat EG-M31B
> >> > Network Media Tank - awesome little machine) that runs some flavor of
> >> > Debian and can be connected to any PC via eSATA as an external HDD's.
> >> > i.e. it exports the built-in HDD as a block device to the host (My
> >> > laptop or PC).
> >> >
> >> > Now, the question is, how can I do this on Linux?
> >> > Would I need a different eSATA card than the on-board eSATA port on
> >> > most motherboards? Or would the on-board one work?
> >>
> >> I suspect your media tank is doing something electrical, like idling its
> >> processor, and re-routing the sata port directly to the internal storage
> >> device, when its in this mode.   I'm unaware of any SATA target drivers
> >> (as opposed to the normal initiator drivers in libata etc)
> >
> > More likely, it is running some custom software the connects to the
> > exposed port (which is probably not a typical PC SATA port -- it would
> > be wired like a Hard Drive's SATA connector (opposite gender, opposite
> > signal directions, etc.).  The custom software presents itself on this
> > port like it was a hard drive and implements some sort of logical hard
> > drive based on the actual internal hard drive -- not really much
> > different from a USB connected mp3 player or camera -- the USB
> > connected mp3 players / camera are just using a different physical
> > interface (USB), but the logic is the same. Again, the USB port on
> > these devices is 'wired' the opposite from the USB port on a normal PC
> > and the logic behind it is also opposite (you cannot really connect a
> > USB port of one PC to the USB port of another -- there is no such thing
> > as a USB 'cross over' (Ethernet) or null-modem (RS232) cable in the USB
> > (or firewire) world). The processor in the little box is implementing
> > much that same sort of processing that goes on inside the micro
> > processor on the controller board of a hard drive -- modern hard drive
> > controller boards are really a full fledged little computer running a
> > very special program that implements the drive end of the mass storage
> > interface (SCSI, SATA, PATA, etc.).  The media tank is just taking this
> > to a different level.
> >
> >>
> >>
> >>
> 
> 
> Sure, I understand what you're saying, but the question is: If they
> can do it with a cheap device like this, then surely one should be
> able todo it with a normal / server motherboard? Obviously they won't
> tell us their secrets, so I need to dig around to see how todo it
> myself. This particular device has a eSATA slave + eSATA Master mode.
> i.e. I can connect another device to this one and they both work
> together, and then when I connect the first one to my PC, I have 2
> HDD's - i.e. a cheap JBOD implementation.


You probably can't do it with 'a normal / server motherboard'.  The SATA
/ eSATA ports on such a board are 'host' ports.  You would need a 'disk'
port, which is *electrically* different -- it is no different than with
USB or Firewire devices.  There is the 'host' side and there is the
'device' side.  They are different.

> 
> 
> I'm trying to see if I can setup  a Linux JBOD on a server chassis
> with say 16 HDD's or something, and then connect it to another server
> via eSATA - i.e. building a cheap scalable SAN.
> 
> 
> 
> P.S. You actually do get USB cross-over cables:
> http://en.kioskea.net/faq/342-connecting-two-computers-with-a-usb-cable
> - they work quite well. They're not as fast a gigabit but works very
> well for older PC's without LAN.
> 
> 

-- 
Robert Heller             -- 978-544-6933 / heller@xxxxxxxxxxxx
Deepwoods Software        -- http://www.deepsoft.com/
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