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?) Â 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. Â 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.). Â 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.). Â 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/ () ascii ribbon campaign -- against html e-mail /\ www.asciiribbon.org -- against proprietary attachments
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