Data Movement: Transporting Partitions for Data Warehousing



            Transporting a partition


  • In this example, we see how to use the transportable tablespaces feature to periodically load data into a large fact table in a data warehousing database.
  • For this, suppose that an enterprise data warehouse has a large table sales.
  • The table is partitioned by date, with data for each month stored in its own partition.
  • In addition, local indexes are build so that you dont have to rebuild global indexes when dropping the oldest partition from the table.
  • Every month you need to load one month of data into the sales table, stored in its own partition.

Set up the fact table: sales. In the data warehouse database (dwr-db).
  • For simplicity, all the initial partitions are kept in the same tablespace.
  • As the oldest partitions are deleted and new are added, eventually each partition will be on its own tablespace.
  • A local index is also created in each partition.

SQL> create table dwr.sales (invoice_no number,
  2    sale_year int not null,
  3    sale_month int not null,
  4    sale_day int not null)
  5  partition by range (sale_year, sale_month, sale_day)
  6    (partition jan05 values less than (2005, 2, 1),
  7     partition feb05 values less than (2005, 3, 1),
  8     partition mar05 values less than (2005, 4, 1),
  9     partition apr05 values less than (2005, 5, 1),
 10     partition may05 values less than (2005, 6, 1),
 11     partition jun05 values less than (2005, 7, 1))
 12     tablespace users;

-- create local index.
SQL> create index dwr.sales_index on dwr.sales(invoice_no) local;

-- Now let's insert some data into table sales.
Run the PL/SQL block below to insert some sample data into sales
declare
 month number :=1;
 day   number :=1;
begin
 for i in 1..30 loop
   insert into dwr.sales values (i, 2005, month, day);
   if mod(i,5) = 0 then
     month := month +1;
     day := day +1;
   end if;
end loop;
end;

-- Check that all partitions (table and index) are in the same tablespace (users):
SQL> select tablespace_name, segment_name, segment_type, partition_name
  2  from dba_segments
  3  where owner = 'DWR';

TABLESPACE_NAME    SEGMENT_NAME    SEGMENT_TYPE       PARTITION_NAME 
------------------ --------------- ------------------ ------------------
USERS              SALES           TABLE PARTITION    JAN05  
USERS              SALES           TABLE PARTITION    FEB05  
USERS              SALES           TABLE PARTITION    MAR05  
USERS              SALES           TABLE PARTITION    APR05  
USERS              SALES           TABLE PARTITION    MAY05  
USERS              SALES           TABLE PARTITION    JUN05  
USERS              SALES_INDEX     INDEX PARTITION    JAN05  
USERS              SALES_INDEX     INDEX PARTITION    FEB05  
USERS              SALES_INDEX     INDEX PARTITION    MAR05  
USERS              SALES_INDEX     INDEX PARTITION    APR05  
USERS              SALES_INDEX     INDEX PARTITION    MAY05  
USERS              SALES_INDEX     INDEX PARTITION    JUN05  

12 rows selected.

Prepare the new data for loading in the warehouse

The month of July has ended and you need to load the July data into the sales table.
In the staging database, perform the steps below:
  1. Create a new tablespace (ts_jul). It will hold the table with july data and will be transported to the data warehouse database.
  2. Create a table jul_sales in the new tablespace. It will hold the july data. jul_sales should have the same structure as the sales table.
  3. Load data on jul_sales table.
  4. Create an index jul_sales_idx on the same columns as the local index on the sales table.
SQL> Create smallfile tablespace ts_jul 
  datafile '/u01/app/oracle/oradata/test112/ts_jul_1.dbf' 
  size 5M logging 
  extent management local 
  segment space management auto; 

SQL> create table hr.jul_sales (invoice_no number,
      sale_year int not null,
      sale_month int not null,
      sale_day int not null)
      tablespace ts_jul;

-- Load July data: (run the pl/sql script)
declare
 day   number :=1;
begin
 for i in 40..70 loop
   insert into hr.jul_sales values (i, 2005, 7, day);
     day := day + 1;
end loop;
end;

-- Create index on jul_sales table: 
SQL> create index hr.jul_sale_idx on hr.jul_sales(invoice_no) tablespace ts_jul;

-- Check table and index location
SQL> select tablespace_name, segment_name, segment_type, bytes
   from dba_segments
   where owner = 'HR'
   order by segment_name, segment_type;
TABLESPACE_NAME   SEGMENT_NAME   SEGMENT_TYPE       BYTES
----------------- --------------- ------------------ ----------
...
TS_JUL            JUL_SALES       TABLE              65536
TS_JUL            JUL_SALE_IDX    INDEX              65536
...


Transport tablespace to the data warehouse database
Perform the steps below:
  1. Make tablespace ts_jul read only
  2. Export metadata of the objects in the tablespace being transported
  3. Copy datafiles to the data warehouse server. Make sure to copy the files to its final location in the server. When you import the tablespace, the paths to the datafiles will be stored in the database.
  4. Copy the export file to the directory pointed by the data_pump_dir object (or to other directory pointed by some directory object in the database)
  5. Import the transported tablespace.
(1) Make tablespace read only
SQL> alter tablespace ts_jul read only;

Tablespace altered.

(2) export metadata
oracle@quark:~$ expdp system dumpfile=expts_jul.dmp directory=data_pump_dir transport_tablespaces=ts_jul logfile=tts_exptsjul.log

Export: Release 11.2.0.1.0 - Production on Fri Oct 08 15:34:45 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
Password: 

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01":  system/******** dumpfile=expts_jul.dmp directory=data_pump_dir transport_tablespaces=ts_jul logfile=tts_exptsjul.log 
Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
Processing object type TRANSPORTABLE_EXPORT/TABLE
Processing object type TRANSPORTABLE_EXPORT/INDEX
Processing object type TRANSPORTABLE_EXPORT/INDEX_STATISTICS
Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
Master table "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_TRANSPORTABLE_01 is:
  /u01/app/oracle/admin/tempdb/dpdump/expts_jul.dmp
******************************************************************************
Datafiles required for transportable tablespace TS_JUL:
  /u01/app/oracle/oradata/tempdb/ts_jul_1.dbf
Job "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully completed at 15:35:35

(3)-(4) Copy export and tablespace data files to the dwr server

(5) Import the tablespace ts_jul to the dwr
oracle@dwr-srv:$ impdp system dumpfile=expts_jul.dmp directory=data_pump_dir transport_datafiles=/u01/app/oracle/oradata/dwr/ts_jul_1.dbf remap_schema=hr:dwr logfile=tts_import.log

Import: Release 11.2.0.1.0 - Production on Fri Oct 08 18:10:20 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
Password: 

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Master table "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01":  system/******** dumpfile=expts_jul.dmp directory=data_pump_dir transport_datafiles=/u01/app/oracle/oradata/dwr/ts_jul_1.dbf remap_schema=hr:crm1 logfile=tts_import.log 
Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
Processing object type TRANSPORTABLE_EXPORT/TABLE
Processing object type TRANSPORTABLE_EXPORT/INDEX
Processing object type TRANSPORTABLE_EXPORT/INDEX_STATISTICS
Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
Job "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01" successfully completed at 18:11:10

-- Check the import
SQL> select count(*) from dwr.jul_sales;

  COUNT(*)
----------
  30


Attach the July data to the Sales table
At this point the tablespace ts_jul has been transported and the table jul_sales is available in the dwr database.
It is not yet, however, available as a partition in the large sales table.
For this we will need to:
  1. Add a partition to the sales table for the July data. This will also create another partition for the local index.
  2. Attach the transported table jul_sales to the table sales by exchanging it with the new partition.
(1) In the dwr server, add a partition to the sales table for the July sales data.
SQL> alter table dwr.sales add partition jul05 values less than (2005, 8,1);

Table altered.

(2) Attach the transported table jul_sales to the table sales by exchanging it with the new partition:
SQL> alter table dwr.sales exchange partition jul05 with table dwr.jul_sales
  2  including indexes 
  3  without validation;

Table altered.
 

  • The exchange partition statement assigns the jul_sales data to the jul05 partition on the sales table.
  • The data is not physically moved to the new partition. Instead database pointers and metadata information are updated.
  • In fact, after the statement executes successfully, you can check that the data is now assigned to the sales table, and the jul_sales table is empty.
SQL> select count(*) from crm1.jul_sales;

  COUNT(*)
----------
  0

SQL> select sale_month, count(*) 
  2  from crm1.sales 
  3  group by sale_month;

SALE_MONTH   COUNT(*)
---------- ----------
  1     5
  6     5
  2     5
  4     5
  5     5
  3     5
  7    31

7 rows selected.

SQL>   select tablespace_name, segment_name, segment_type, partition_name
  2    from dba_segments
  3    where owner = 'DWR';

TABLESPACE_NAME   SEGMENT_NAME   SEGMENT_TYPE    PARTITION_NAME
----------------- -------------- --------------- ------------------------------
USERS             SALES          TABLE PARTITION  JAN05
USERS             SALES          TABLE PARTITION  FEB05
USERS             SALES          TABLE PARTITION  MAR05
USERS             SALES          TABLE PARTITION  APR05
USERS             SALES          TABLE PARTITION  MAY05
USERS             SALES          TABLE PARTITION  JUN05
TS_JUL            SALES          TABLE PARTITION  JUL05
USERS             SALES_INDEX    INDEX PARTITION  JAN05
USERS             SALES_INDEX    INDEX PARTITION  FEB05
USERS             SALES_INDEX    INDEX PARTITION  MAR05
USERS             SALES_INDEX    INDEX PARTITION  APR05
USERS             SALES_INDEX    INDEX PARTITION  MAY05
USERS             SALES_INDEX    INDEX PARTITION  JUN05
TS_JUL            SALES_INDEX    INDEX PARTITION  JUL05

14 rows selected.
  • You can now drop jul_sales table.
  • You can also, if needed, make the tablespace ts_jul read write.
SQL> alter tablespace ts_jul read write;

Tablespace altered.

Data Movement: Transporting Tablespaces


            Transporting tablespaces

Requirements:
  • Oracle 8i or later: Enterprise Edition required to generate a transportable tablespace set
  • Since 9i: Block size may be different across Databases
  • Since 10g: Tablespaces can be transported across platforms (both databases need to have the COMPATIBLE parameter set to at least 10.0.0)
  • Since 11gR1: You must use DataPump utilitties (expdb, impdp) to transport tablespaces

When to use:
  • To export/import partitions of large tables (see example here)
  • For publishing structured data on CDs
  • Copying multiple read-only version of a tablespace to multiple databases
  • Archive historical data
  • Perform tablespace point-in-time recovery

Procedure for Transporting a tablespace set:
  1. Determine the Transportable Set. A transportable set is formed by the datafiles of all tablespaces being transported plus the export file containing metadata for the entire set.
  2. Check that the transportable set is self-contained (there should be no references from objects within the tablespace set to objects outside the set).
  3. If you will be migrating across platforms, check whether you will need to convert the datafiles for the same endianess.
  4. Make the tablespaces that will be transported READ ONLY
  5. Export the metadata for the transportable set
  6. Copy the datafiles and export file to the destination host.
  7. Import the metadata and datafiles
  8. Make tablespaces READ WRITE


Transporting tablespaces. Example:

(1) Check the endian format of both platforms (if they are different):

Query the V$TRANSPORTABLE_PLATFORM view to see the platforms that are supported, and to determine each platform's endian format (byte ordering).
You can check the endian_format for your specific platform:
SQL> select d.platform_name, endian_format
  2  from v$transportable_platform tp, v$database d 
  3  where tp.platform_name = d.platform_name;

PLATFORM_NAME                            ENDIAN_FORMAT
---------------------------------------- --------------
Linux IA (32-bit)                        Little

(2) setup the tablespaces to be transported.
This example create two tablespaces on database DB1. It creates a table and index on the tablespaces to be transported to database DB2.
SQL> Create smallfile tablespace HR1 
  datafile '/u01/app/oracle/oradata/db1/hr1_1.dff' 
  size 5M logging 
  extent management local 
  segment space management auto; 

SQL> Create smallfile tablespace HR2 
  datafile '/u01/app/oracle/oradata/db1/hr2_1.dbf' 
  size 5M reuse autoextend on next 1m maxsize 10m logging 
  extent management local 
  segment space management auto; 

SQL> create table hr.hr_emp
  2  tablespace hr1
  3  as select * from hr.employees;

SQL> create index hr.idx_hr_emp 
     on hr.hr_emp(first_name, last_name)
     tablespace hr2;

SQL> alter table hr.hr_emp
  2  add constraint fk_hr_emp_dept
  3  foreign key (department_id) references hr.departments(department_id);

-- check the location of the created objects.
-- We'll transport HR1 and HR2 between two Oracle 11gr2 running on Linux 32-bit.
SQL>  select owner, segment_name, segment_type, tablespace_name
  2  from dba_segments
  3  where tablespace_name in ('HR1', 'HR2');

OWNER   SEGMENT_NAME    SEGMENT_TYPE       TABLESPACE_NAME
------- --------------- ------------------ ------------------------------
HR      HR_EMP          TABLE              HR1
HR      IDX_HR_EMP      INDEX              HR2

(3) Select the self-contained tablespace set.
  • You can only transport a self-contained tablespace set, which means that there may be no references from an object inside the set of tablespaces to another tablespace not included in the set.
  • In our example, because table HR_EMP on tablespace HR1 has an index on tablespace HR2, both tablespaces need to be transported.
  • In addition, since HR.HR_EMP has a foreign key references to HR.DEPARTMENTS (in another tablespace) the third tablespace should also be included in the set. Otherwise a violation will occur.

Violations of self-containement can be caused by:
  • Index inside the set belongs to table outside the set
  • Partitioned tables has a partition outside the set
  • Referential integrity constraint points to table outside the set
  • Table has a LOB column that point to LOBs outside the set






(4) Check if set is self contained.
  • Use DBMS_TTS.TRANSPORT_SET_CHECK to validate the set of tablespaces.
  • If any violation if found it will be listed in the TRANSPORT_SET_VIOLATIONS view.
  • In this case, HR.HR_EMP has a foreign key referencing HR.DEPARTMENTS (in tablespace EXAMPLE). An violation will be found, since we are not including the third tablespace in the transportable set.
SQL> execute dbms_tts.transport_set_check('hr1, hr2', true);
        
PL/SQL procedure successfully completed.

SQL> select * from transport_set_violations;

VIOLATIONS
----------------------------------------------------------------------------------------------------
ORA-39906: Constraint FK_HR_EMP_DEPT between table HR.DEPARTMENTS in tablespace EXAMPLE and table HR.HR_EMP in tablespace HR1.

So let's drop the foreign key constraint: 

SQL> alter table hr.hr_emp drop constraint fk_hr_emp_dept;
Table altered.

(4) Make tablespaces read only
SQL> alter tablespace hr1 read only;
SQL> alter tablespace hr2 read only;

(5) Invoke data pump as system and export the tablespace in the transportable set.
  • directory: IS the directory objects pointing the directory where you want the export file to be generated.
  • transport_tablespaces: parameter indicating a transportable tablespace export. Only the metadata for the tables and dependent objects within the transportable set are exported.
oracle@quark:~$ expdp system dumpfile=exphr1_2.dmp directory=data_pump_dir transport_tablespaces=hr1, hr2 logfile=tts_exphr1_2.log

Export: Release 11.2.0.1.0 - Production on Thu Oct 07 15:22:51 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
Password: 

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01":  system/******** dumpfile=exphr1_2.dmp directory=data_pump_dir transport_tablespaces=hr1, hr2 logfile=tts_exphr1_2.log 
Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
Processing object type TRANSPORTABLE_EXPORT/TABLE
Processing object type TRANSPORTABLE_EXPORT/INDEX
Processing object type TRANSPORTABLE_EXPORT/INDEX_STATISTICS
Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
Master table "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_TRANSPORTABLE_01 is:
  /u01/app/oracle/admin/db1/dpdump/exphr1_2.dmp
******************************************************************************
Datafiles required for transportable tablespace HR1:
  /u01/app/oracle/oradata/db1/hr1_1.dff
Datafiles required for transportable tablespace HR2:
  /u01/app/oracle/oradata/db1/hr2_1.dbf
Job "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully completed at 15:24:01 

(6) If the tablespaces are being transported to a different platform, you need to convert the datafiles before copying them.
For example, if the destination database in on a Windows machine, then:
oracle@quark:/$ rman target /

Recovery Manager: Release 11.2.0.1.0 - Production on Thu Oct 07 15:31:55 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: DB1 (DBID=64992127)

RMAN> convert tablespace hr1, hr2
2> to platform 'Microsoft Windows IA (32-bit)' 
3> format '/tmp/%U'; 

Starting conversion at source at 07-Oct-10
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=18 device type=DISK
channel ORA_DISK_1: starting datafile conversion
input datafile file number=00007 name=/u01/app/oracle/oradata/db1/hr1_1.dff
converted datafile=/tmp/data_D-DB1_I-54881118_TS-HR1_FNO-6_01mrt1cn
channel ORA_DISK_1: datafile conversion complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting datafile conversion
input datafile file number=00008 name=/u01/app/oracle/oradata/db1/hr2_1.dbf
converted datafile=/tmp/data_D-DB1_I-54881118_TS-HR2_FNO-7_02mrt1co
channel ORA_DISK_1: datafile conversion complete, elapsed time: 00:00:01
Finished conversion at source at 07-OCT-10

(7) Transport the Tablespace set
  • Step 1: Copy the export file to the directory pointed by the DATA_PUMP_DIR directory object
  • Step 2: Copy the data files to the location of the existing datafiles of the destination database.

(8) Import the tablespaces
oracle@proton:$ impdp system dumpfile=exphr1_2.dmp directory=data_pump_dir transport_datafiles=/u01/app/oracle/oradata/DB2/hr1_1.dff, /u01/app/oracle/oradata/DB2/tts/hr2_1.dbf remap_schema=hr:crm1 logfile=tts_import.log

Import: Release 11.2.0.1.0 - Production on Thu Oct 07 17:18:56 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
Password: 

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Master table "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01":  system/******** dumpfile=exphr1_2.dmp directory=data_pump_dir transport_datafiles=/u01/app/oracle/oradata/DB2/hr1_1.dff, /u01/app/oracle/oradata/DB2/hr2_1.dbf remap_schema=hr:crm1 logfile=tts_import.log 
Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
Processing object type TRANSPORTABLE_EXPORT/TABLE
Processing object type TRANSPORTABLE_EXPORT/INDEX
Processing object type TRANSPORTABLE_EXPORT/INDEX_STATISTICS
Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
Job "SYSTEM"."SYS_IMPORT_TRANSPORTABLE_01" successfully completed at 17:19:16

-- Check the imported tablespaces
SQL> select owner, segment_name, segment_type, tablespace_name
  2  from dba_segments
  3* where tablespace_name in ('HR1' , 'HR2');

OWNER    SEGMENT_NAME         SEGMENT_TYPE       TABLESPACE_NAME
-------- -------------------- ------------------ ------------------------------
CRM1     HR_EMP               TABLE              HR1
CRM1     IDX_HR_EMP           INDEX              HR2

Configuring NFS on Ubuntu


How NFS works:
Typically, NFS allows a client machine (quark) to require transparent access to data stored on a server machine (dirak).
For this to take place successfully:
  1. The server (dirak) runs NFS daemon processes (nfsd and mountd) in order to make its data available to clients.
  2. The sysadmin determines what to make available, and exports names and parameters of directories to be shared, normally using the /etc/exports configuration file and the exportfs command.
  3. The sysadmin configures the server (using hosts.deny, hosts.allow) so that it can recognize and approve validated clients.
  4. The client machine requests access to exported data, typically by issuing a mount command.

Client quark mounts the /usr/home directory from host dirac on the local directory /home
# mount -t nfs dirac:/usr/home/ /home
To mount the remote directory:
  1. mount connects to mountd daemon, running on dirac.
  2. mountd checks whether quark has permission to mount /usr/home. If so, it returns a file handle.
  3. When someone tries to access the file /home/jdoe/login.sh in quark, the kernel places an RPC call to nfsd on the NFS server (dirac):
    • rpc_call(file handle, file name, UID, GID) - User and Group IDs must be the same on both hosts.














  1. If all goes well, users on the client machine can then view and interact with mounted filesystems on the server within the parameters permitted.

  • Client and server NFS functionality is implemented as kernel-level daemons that are started from user space at system boot.
  • These NFS daemons are normally started at boot time and register themselves with the portmapper, a service that manages the access to TCP ports of programs involved in remote procedure calls.
    • mountd - Runs on the NFS Server. Processes client's NFS requests.
    • nfsd (NFS daemon) - Runs on the NFS Server. Service the client's request.


Installing and Configuring NFS Server:
(Step 1): Check whether your kernel has NFS support compiled in. One way to do this is to query the kernel interface on the proc filesystem.
$ cat /proc/filesystems | grep nfs
nodev   nfs
nodev   nfs4
nodev   nfsd

-- If Kernel support for NFS is installed, you should see the lines above. 
-- If no results are displayed, you need to install NFS Server support:

$ sudo apt-get install portmap nfs-kernel-server

(Step 2): Configure NFS Server: define shared directories
  • Now you need to tell the NFS server which directories should be available for mounting, and which parameters should control client access to them.
  • You do this by exporting the files, that is, listing filesystems and access controls in the /etc/exports file.
# exports file for dirac. 
# Each line defines a directory and the hosts allowed to mount it

/home      quark.math.usm.edu(rw, sync)  proton.math.usm.edu(rw, sync)
/usr/TeX   *.math.usm.edu
/home/ftp  *(ro)
In the exports file above:
  • *.math.usm.edu -- matches all hosts in teh domain math.usm.edu
  • Security options:
  • rw - allow read/write in the exported file. Disallowed by default.
  • sync - Reply to requests only after changes have been committed to stable storage.

(Step 3): export the shares.
After modifying /etc/exports, run the command
$ sudo exportfs -ra 

(Step 4): Edit /etc/default/portmap to enable access to portmap from remote machines.
By default, portmap listens only for RPC calls coming from the loopback interface (127.0.0.1). For this,
(a) comment the "-i 127.0.0.1" entry in the file;
(b) restart portmap; and
(c) restart the NFS kernel server:
edit /etc/default/portmap
S sudo /etc/init.d/portmap restart
$ sudo /etc/init.d/nfs-kernel-server restart


Configuring NFS Clients

(Step 1): Install NSF Client
$ sudo apt-get intsall portmap nfs-common

(Step 2 - optional): Configure portmap to allow connections to the NFS server.

/etc/hosts.deny - list of hosts that are not allowed to access the system. Edit the file to block all clients. In this sense, only those that you explicitly authorize (in /etc/hosts.allow) will be able to connect the server.
portmap: ALL
/etc/hosts.allow - list of hosts authorized to access the server
portmap: <nfs Server IP address>

Mounting a remote filesystem manually:
From the client:
$ sudo mount dirac.math.usm.edu:/users/home /home

Configure auto mounting during startup:
  • You can set up automatic nfs mounting by including entries in /etc/fstab.
  • The /etc/fstab file is used to statically define the file systems that will be automatically mounted at boot time.
  • It contains a list of all available disks and disk partitions, and indicates how they are to be initialized into the overall system's file system
  • During machine startup, the mount program reads /etc/fstab file to determine which options should be used when mounting the specified device.
# device name   mount point     fs-type      options       dump-freq pass-num                                          
# servername:dir /mntpoint        nfs          rw,hard,intr   0         0

dirac:/users/home  /home  nfs  rw, hard, intr  0  0 
Just like other /etc/fstab mounts, NFS mounts in /etc/fstab have 6 columns, listed in order as follows:
  • The filesystem to be mounted (dirac.math.usm.edu:/users/home/)
  • The mountpoint (/home)
  • The filesystem type (nfs)
  • The options (rw, hard, intr)
  • Frequency to be dumped (a backup method) (0)
  • Order in which to be fsck'ed at boot time. (0) - dont perform fsck.

Options:
  • rw - read/write
  • hard - share mounted so that if the server becomes unavailable, the program will wait until the server is available again.
See more details on man mount