Why is an nfs server mounted as rw returning read only filesystem errors

'Read-only file system' error indicates that the file system is exported as read only. The rw mount option tells client that 'WRITE' is allowed to be sent to the server. On regular unix systems, check /etc/exports file:

/NFS2 172.x.y.z(rw)

on appliances, check the documentation to export as read-write.

Export of a parent folder (ro) will override a child export (rw).

Example exports:

/NFS_ROOT *(ro)
/NFS_ROOT/SHARE1 *(rw)

SHARE1 will be read-only because NFS_ROOT is read-only. You have constraints on an exported root directory which may be causing the problem.

As Brian said, a parent export can override a child export. But you can solve this by adding priorities to your exports. So, using Brian's example, this would solve the problem:

/NFS_ROOT *(ro,fsid=2)
/NFS_ROOT/SHARE1 *(rw,fsid=1)