Discussions about the enhanced version of linux' Network Block Devices

Volker Stoppe | 4 Nov 2008 00:29

client (-1) cannot open NBD device /dev/nda or similar: No such file or directory

Hallo list!

I am trying to implement ENBD but I stuck at the moment when I want to connect from the client to the Server.
Compiation of the source works fine, the modules are loading without a problem and I have no problem
starting with the server. I would be -very- glad if someone could help! Nobody in the web seems to have my
problem. I followed the instructions from: http://www.it.uc3m.es/~ptb/nbd/ but there has to be
something missing. It is definitly not sudo (installed).

Environment:
Distri: Debian 4.0
Kernel: 2.6.18-6-686
ENBD: 2.4.35

PS: I know that client and server have the same hostname (clones).

Some output of the Systems:

== Server ==
debian32:~/enbd# lsmod | grep enbd
enbd_ioctl              5920  0
enbd                  583032  1 enbd_ioctl

debian32:~/enbd# ./enbd-server 4001 /dev/sda1
enbd-server[3843]: server: will open resources in mode linear
enbd-server[3843]: looking for blksize of /dev/sda1 with fstat...
enbd-server[3843]: blksize of /dev/sda1 is 4096                  
enbd-server[3843]: set final blksize of whole resource to 4096   
enbd-server[3843]: looking for size of fd 4 with seek SEEK_END...
enbd-server[3843]: set size of fd 4 to 98668544                  
enbd-server[3843]: server: set blksize to 4096.

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Peter Breuer | 4 Nov 2008 16:23

Re: client (-1) cannot open NBD device /dev/nda or similar: Nosuch file or directory

Hi Volker ...

"Also sprach Volker Stoppe:"
> Hallo list!
> 
> I am trying to implement ENBD but I stuck at the moment when I want to
> connect from the client to the Server.  Compiation of the source works
> fine, the modules are loading without a problem and I have no problem
> starting with the server.  I would be -very- glad if someone could help!
> Nobody in the web seems to have my problem.  I followed the instructions
> from: http://www.it.uc3m.es/~ptb/nbd/ but there has to be something
> missing.  It is definitly not sudo (installed).

Strange. Let's see (log output and /proc/nbdinfo is what I generally
need to make diagnosis complete - te's have a go).

> Environment:
> Distri: Debian 4.0
> Kernel: 2.6.18-6-686
> ENBD: 2.4.35
> 
> PS: I know that client and server have the same hostname (clones).
> 
> Some output of the Systems:
> 
> == Server ==
> debian32:~/enbd# lsmod | grep enbd
> enbd_ioctl              5920  0
> enbd                  583032  1 enbd_ioctl
>

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Volker Stoppe | 10 Nov 2008 13:27

Re: client (-1) cannot open NBD device /dev/nda or similar: Nosuch file or directory

Hallo together!

I want to mirror a few server over the network to target mashines via  
enbd/mdadm. If FR1 was developed for notebook users to do spontaneous  
intellient RAID1 mirroring with an externel device, it should also be  
suitable for my scenario.

Question: Is it possible to mirror the local disks without reorganizing  
them? I want to keep the structure of partitions and volumes. The best  
thing would be a copy on write mechanism to the target machine by the enbd  
/ /dev/nda -device. A kind of daemon observing changes on /dev/sda and  
mirroring it to /dev/nda(x) would be fine.
Does anyone know a solution? Googling didn't help very much.

Greetinx

On Tue, 04 Nov 2008 16:23:50 +0100, Peter Breuer  
<P.T.Breuer <at> cs.bham.ac.uk> wrote:

>> enbd-client[6057]: enbd-client #5757 main[0]: client (-1) cannot open  
>> NBD device /dev/nda or similar: No such file or directory
> Oh - well, that's clear!
> You don't have the /dev/nda, /dev/ndaS, /dev/ndaX, /dev/ndaSX devices
> nodes.
> You need to make them .. there's a MAKEDEV script provided.

This helped! I should have read the section about testing more closelay. A  
reference to MAKEDEV in the Chapter Howto-2 would be helpful.

--

--

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Peter Breuer | 10 Nov 2008 14:21

Re: client (-1) cannot open NBD device /dev/nda or similar:Nosuch file or directory

"Also sprach Volker Stoppe:"
> I want to mirror a few server over the network to target mashines via  
> enbd/mdadm. If FR1 was developed for notebook users to do spontaneous  
> intellient RAID1 mirroring with an externel device, it should also be  
> suitable for my scenario.

Yes, but the FR1 code and designs moved into standard kernel softRAID ages
ago. About the only thing that didn't go in was the communication back
to the raid device from the enbd device when the enbd device felt ill
or got well again. But one can do that with udev nowadays (enbd signals
udev with the information .. the enbd udev rules file tells raid what
to do with the info, or can do, I've forgotten if it needs editing to
suit ...)

> Question: Is it possible to mirror the local disks without reorganizing  

I'm not sure what you mean .. is this a question about raid? I.e., can
linux soft raid mirror devices without requiring reformatting them? The
answer is more complex than a simple yes/no, it's something like "99%
yes" and "1% no".

That's essentially because what raid "formatting" exists is in the form
of a 64KB block after the end of the data area on the raided device (i.e.
just before the end of the data are on the underlying device). If your
"devices" are partitions of a disk, then they very likely have 64KB of
free space after the end of the partition and before the start of the
next partition, and you should expand the underlying partition size by
64KB (without changing the FS size on it at all!). That just means
playing with the partition-end numbers in fdisk and rebooting.

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