[linux-lvm] Does LVM work with NBD?

["ASHISH GUPTA" <ashish_gupta@infy.com>]

Hi All,

 

1) I'm using NBD and LVM . I have mounted the remote device

using NBD(version 2.4.27). When I do pvcreate on mounted disk,it is successful.

 

#pvcreate /dev/nb0

pvcreate -- physical volume "/dev/nb0" successfully created

 

But when we try out other commands such as pvdisplay, vgcreate etc. it gives the

following error.

 

 #pvdisplay /dev/nb0
pvdisplay -- ERROR "pv_read(): pv_create_name_from_kdev_t" no VALID physical volume "/d
ev/nb0"

 

# ./vgcreate /dev/nb0
vgcreate -- please enter physical volume name(s)

 

pvcreate uses the information from /proc/partitions.

It  works although the /proc/partitions is not updated with the remote device information.

However the other LVM commands like "vgcreate", "pvdisplay" look for remote device

information in /proc/partition and as the entry is not there in dir_cache, it fails.

 

To make it run, I have added a entry for nb0 in the file lvm_dir_cache.c in _noprocdir.

/* devices *not* showing up in /proc/partitions must be scanned anyway */
static char *_noprocdir[] = {
        LVM_DIR_PREFIX "loop",
        LVM_DIR_PREFIX "nb0",
        NULL
};

 

After doing,I am able to do pvcreate, vgcreate and so.Is it right way to do this?

 

2)As per some mail in lvm-linux archieve, if I make an entry for nbd device in _devdir[] in file lvm_dir_cache.c

 and just modify this following check by replacing _cache_size with '1'.Still pvcreate fails.And it gives the following error.

 

if(!_cache_size)
                        _scan_devs( TRUE);
                else
                        _scan_devs( FALSE);
        }

 

 

# pvcreate /dev/nb0

"/dev/nb0 has a partition table"

 

 

3) Is there any patch available to make NBD working with LVM?

 

 

 

Regards,

Ashish