nbd troubles

marco.hahn · 09-21-2010, 03:28 PM

Hi, I'm thinking of a new DVD-less system and may occasionally need to use the DVD of another system. I thought that nbd would be a good choice.

But alas: On the server with the DVD (Gentoo 2006.1), I start nbd-server (2.8.2) with

Code:

nbd-server 55433 /dev/hdc -l 192.168.83.240

and on the client (Ubuntu 10.4), I start nbd-client (2.9.14) with

Code:

sudo nbd-client 192.168.83.11 55433 /dev/nb0

However, all I get is this error message:

Code:

Error: Cannot open NBD: No such file or directory
Please ensure the 'nbd' module is loaded.

Unfortunately, Google is not a great help, as there are almost no results for these messages. Anyone has any idea?

Thanks,
marco.hahn

Chuck56 · 09-22-2010, 08:14 AM

NBD consists of a kernel module and userspace programs. The error you're showing says that the kernel module is not loaded. It only needs to be loaded on the machine running nbd-client, not nbd-server.

I run Slackware but these commands should be available on either Gentoo or Ubuntu.

To verify check the machine that is running nbd-client:

Code:

lsmod | grep nbd

To load it manually on the nbd-client machine:

Code:

modprobe nbd

marco.hahn · 09-22-2010, 01:27 PM

I forgot to mention in my first post, but nbd is loaded.

Chuck56 · 09-22-2010, 01:30 PM

Quote:

Originally Posted by marco.hahn

Code:

sudo nbd-client 192.168.83.11 55433 /dev/nb0

However, all I get is this error message:

Code:

Error: Cannot open NBD: No such file or directory
Please ensure the 'nbd' module is loaded.

...then check to see if sudo is setup correctly for nbd-client

rojoblandino · 06-26-2013, 05:07 PM

I am having same problem:

Code:

root@api:~# nbd-client 192.168.1.81 1043 /srv/nbd/disk1
Error: Cannot open NBD: No such file or directory
Please ensure the 'nbd' module is loaded.
Exiting.

Code:

root@api:~# lsmod  | grep nbd
nbd                     8001  0

And my logs shows following:

Code:

Jun 26 15:02:51 api nbd_client[6744]: Cannot open NBD: No such file or directory#012Please ensure the 'nbd' module is loaded.
Jun 26 15:02:51 api nbd_client[6744]: Exiting.

rojoblandino · 06-26-2013, 05:37 PM

Quote:

Originally Posted by rojoblandino

I am having same problem:

Code:

root@api:~# nbd-client 192.168.1.81 1043 /srv/nbd/disk1
Error: Cannot open NBD: No such file or directory
Please ensure the 'nbd' module is loaded.
Exiting.

Code:

root@api:~# lsmod  | grep nbd
nbd                     8001  0

And my logs shows following:

Code:

Jun 26 15:02:51 api nbd_client[6744]: Cannot open NBD: No such file or directory#012Please ensure the 'nbd' module is loaded.
Jun 26 15:02:51 api nbd_client[6744]: Exiting.

I am using debian squeeze and made it work succesfully, the trick is filling the file /etc/nbd-client

Code:

NBD_DEVICE[0]=/dev/nbd1
#
# Type; s=swap, f=filesystem (with entry in /etc/fstab), r=raw (no other setup
# than to run the client)
NBD_TYPE[0]="r"
#
# The host on which the nbd-server process is running
NBD_HOST[0]="192.168.1.81"
#
# The port on which this client needs to connect
NBD_PORT[0]="1043"
#
# Any extra parameters you would want to specify
NBD_EXTRA[0]=

And woala, it worked:

Code:

root@api:~# /etc/init.d/nbd-client start
Starting NBD client process: Connecting...Negotiation: ..size = 20971520KB
bs=1024, sz=20971520
connected /dev/nbd1
Activating...
/dev/nbd1: raw selected. doing nothing.
nbd-client.

In few works the nbd-client work but with the file not directly with the command.

rojoblandino · 06-27-2013, 05:50 PM

I have made succesfully a RAID with nbd drives, but after placing it under production i did some tests.

1) When a cluster server of one of the nbd being in the RAID is shutdown or network goes off. The mdadm takes 15 minutes to response when a check is done the console goes in blank and no response is given around 15 minutes. Then the mdadm give output normally showing that a nbd drive is faulty spare.

2) To re-attach the nbd drive the RAID must be unmounted then stopped, and nbd-client must be restarted.

3) Then RAID recovery procedures must be followed normally.

I did not experience any problem using RAID6 over nbd, the info keeps consistent and nbd answer very well, the only inconvenient is the 15 minutes mdadm takes to show the results when a failure occurs.

Having a RAID over nbd not shure what happen if switch is off. Shurely data may be lost a good backup always will be needed.