Multiple serial consoles via null modem cable

[Charles Sprickman]

On Tue, 12 Jan 2010, Jeremy Chadwick wrote:

> On Tue, Jan 12, 2010 at 02:50:29PM -0500, Charles Sprickman wrote:
>> On Tue, 12 Jan 2010, Charles Sprickman wrote:
>>
>>> On Jan 12, 2010, at 12:04 PM, Boris Samorodov <bsam at ipt.ru> wrote:
>>>
>>>> On Tue, 12 Jan 2010 17:14:44 +0200 Marin Atanasov wrote:
>>>>
>>>>> I'm thinking about the following situation - 1 system acting like a host
>>>>> with a serial port hub, each port of the hub is connected to a different
>>>>> machine on sio0, using null modem cables.
>>>>
>>>> Along with milti-io serial cards we use multi-usb serial
>>>> converters, such as SUNIX UTS7009P (7 USB to serial adapter):
>>>> http://www.sunix.com.tw/it/en/LinkCraft/UTS4009P_UTS7009P.htm
>>>>
>>>
>>> I need to look it up when I'm in front of a real computer, but
>>> there are a number of reasonably priced multport USB to serial
>>> converters out there.
>>
>> Here we go:
>>
>> http://www.usbgear.com/USB-Serial.html
>>
>> Some very cool stuff there.  They also list the chipset used in some
>> of those so you have some idea if it will work with FreeBSD.  I
>> think Vixie originally pointed me to this model:
>>
>> http://www.usbgear.com/computer_cable_details.cfm?sku=USB-16COM-RM&cats=199&catid=493%2C494%2C474%2C199%2C461%2C106%2C1009%2C601
>>
>> If anyone has the lowdown on which chipsets generally work with
>> FreeBSD (especially with all the changes in 8.0), that would be
>> great.
>
> The same device appears here:
>
> http://www.serialgear.com/USB-16COM-RM.html
> http://www.allserial.com/usb_16com-rm.html

Damn, $130 more than usbgear.com...

> Quite inexpensive compared to an actual serial console server!

Very much so!  And if you already have a sort of "utility box" in a rack, 
this makes a nice add-on.  There are some very cheap 4 and 8 port models 
as well.

> I had no idea such a device existed (well, USB-to-serial adapters, sure, 
> just not ones which housed 16 adapters or was rack-mountable.  :-) ).

Who knows what's inside, there are two USB hubs in there...  But yeah, 
rack-mount and AC power are nice.

> Decently sized FIFO buffers as well (128/384 byte Tx/Rx), at least 
> compared to a classic 16650A (14/16 byte Tx/Rx).  Usually larger FIFO == 
> can handle higher bps without character loss.
>
> I've 5 questions about this device:
>
> * Does it work with/use hardware flow control (CTS/RTS)?

Yes.  There were a few machines that were giving me issues with the old 
3-wire RocketPort card we had (which only had 8 ports, cost more *used* 
than this USB thing cost new, had buggy drivers, and only had a 3-wire 
interface) and they worked fine when moved to this device.

> * Have you tested it for character loss at 115200bps rates?

Nope, never had much luck getting everything (BIOS, loader, getty) all 
talking at the same speed, so I just leave it at 9600.  Zero issues 
though...

> * How do you configure each port (speed, flow, etc.)?

I let conserver deal with that - I set the baud, parity and "options" in 
the default stanza for all ports.  It apparently does the "right thing" 
when opening the port.  Again, zero issues.

> * Does it work under FreeBSD 8.x (given that the entire USB stack
>  was re-written)?

No idea, don't even have an 8.x machine at that site.  If you have any 
contacts over at ISC, you might ask there, I got the impression from Vixie 
that this device became part of their standard co-lo build.

> * Do you have any idea what the power usage is on this device (in amps)?
>  (Our MRV claims 1A max, but drives about 0.25A or so).

No clue, but I imagine it's negligible.  The device generates almost no 
heat, and all of that is in the area around the power supply.

>> The above model works great on an old 4.11 box.  It's an FTDI
>> chipset - at the very bottom of the page they even claim FreeBSD and
>> OpenBSD support.
>>
>> dmesg:
>>
>> uhub2: Genesys Logic USB Hub, class 9/0, rev 1.01/0.11, addr 2
>> uhub2: 7 ports with 7 removable, self powered
>> ucom0: FTDI USB FAST SERIAL ADAPTER, rev 2.00/5.00, addr 3
>> [...]
>> ucom11: FTDI USB FAST SERIAL ADAPTER, rev 2.00/5.00, addr 8
>> [...]
>> uhub3: Genesys Logic USB Hub, class 9/0, rev 1.01/0.12, addr 9
>> uhub3: 4 ports with 4 removable, self powered
>> ucom12: FTDI USB FAST SERIAL ADAPTER, rev 2.00/5.00, addr 10
>> [...]
>> ucom15: FTDI USB FAST SERIAL ADAPTER, rev 2.00/5.00, addr 11
>
> Very nice -- the fact they're using FTDI chips is good (from what I
> understand of USB-to-serial adapters).

Yep, this was all plug-and-play.  I also found a source for db9-db9 null 
modem cables at about $3 a pop - much simpler than building rj-xx to db9 
adapters (xyplex, rocketport) or dealing with giant harnesses (cisco, 
xylogics).

>>> We have a 16 port model that's rack mounted and cost around $400.
>>> It works better many of the more expensive multiport serial cards.
>>> Paired with conserver, it's a really nice solution.  Conserver's
>>> logging is great...
>>>
>>> I've used old dedicated terminal servers in the past and they can
>>> be a pain to deal with.  The newer ones are probably nicer, but
>>> are also lots of money.
>
> Classic devices (like the Portmaster) are indeed a pain in the butt to
> deal with.  I've no experience with Ciscos, but in the case of the PM,
> documentation vs. implementation mismatch galore.  The MRV devices are
> thoroughly documented (it borders on overwhelming -- I'd say half of the
> configuration parameters are foreign to me), and I think the Cyclades TS
> devices are as well; it's the cost of the Cyclades which blows my mind
> (zero justification for it too, other than "enterprise cost mentality",
> e.g. charge as much as possible because large businesses will pay it).

I had surplus junk from the dialup days - Xylogics Annex boxes and Xyplex 
boxes.  Both suck in so many ways that they aren't even worth using.  The 
Annex stuff is still stuck in my brain, wasting valuable space.

> I think for folks who want a multiport serial console device that sits
> on Ethernet, the MRV or Cyclades device would be a good choice, since
> it's a standalone unit which doesn't need to be physically cabled to a
> "host" box (and often a good choice for those who want modem-based OOB
> access to devices, since it can house a v.90 modem).  For those with
> less requirements and want to spend less, the above USB-to-serial device
> looks fantastic -- and at almost 1/4th the cost of our MRV.  :-)

Hey, get an Alix board, slap it in a case with a CF card and put FreeBSD 
and conserver on there.  Plug an old Courier into one of those serial 
ports and setup ppp for dial access.  You'd still beat the cost of any 
"appliance" and have something that's just as reliable.  Conserver is what 
really makes this a plug-and-play setup - it's very easy to get going and 
it "just works".

> As usual, thanks for the insights, Charles!

Thank Vixie and ISC, they're the ones that found this device and the 
usbgear.com guys...

C

> -- 
> | Jeremy Chadwick                                   jdc at parodius.com |
> | Parodius Networking                       http://www.parodius.com/ |
> | UNIX Systems Administrator                  Mountain View, CA, USA |
> | Making life hard for others since 1977.              PGP: 4BD6C0CB |
>
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