What You See Is What You Get Element

Playing with ZFS Shadow Migration

In Oracle Solaris 11.1

by Alexandre BorgesOracle ACE

Part 3 of a series that describes the key features of ZFS in Oracle Solaris 11 and provides step-by-step procedures explaining how to use them. This article describes the Shadow Migration feature and shows how to use it to migrate data from one system to another system.


Published June 2014


right arrow Part 1 - Using COMSTAR and ZFS to Configure a Virtualized Storage Environment
right arrow Part 2 - Playing with Swap Monitoring and Increasing Swap Space Using ZFS Volumes
right arrow Part 3 - Playing with ZFS Shadow Migration
right arrow Part 4 - Delegating a ZFS Dataset to a Non-Global Zone
right arrow Part 5 - Playing with ZFS Encryption
right arrow Part 6 - Playing with ZFS Snapshots
right arrow Part 7 - Configuring SMB Sharing

Imagine that we have some data on an older server running Oracle Solaris 11, and we need to migrate this data to a new server running Oracle Solaris 11.1. This is a classic case where we could use a new feature of Oracle Solaris 11 called Shadow Migration. Shadow Migration can also be used to migrate data from systems running Oracle Solaris 10 releases.

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Using Shadow Migration is very easy; for example, we could migrate shared ZFS, UFS, or VxFS (Symantec) file systems through NFS or even through a local file system.

To simulate an example of using Shadow Migration to migrate data between two systems, we're going to use two virtual machines that have Oracle Solaris 11 installed (solaris11-1 and solaris11-2) in a virtual environment provided by Oracle VM Virtual Box. Furthermore, in the solaris11-2 host, we're going to share a file system (/solaris11-2-pool/migrated-filesystem) and migrate the data inside this file system to the solaris11-1 host.

The first step of this procedure is installing the shadow-migration package:

root@solaris11-1:~# pkg install shadow-migration
           Packages to install:  1
       Create boot environment: No
Create backup boot environment: No
            Services to change:  1

DOWNLOAD                                PKGS         FILES    XFER (MB)   SPEED
Completed                                1/1         14/14      0.2/0.2  126k/s

PHASE                                          ITEMS
Installing new actions                         39/39
Updating package state database                 Done
Updating image state                            Done
Creating fast lookup database                   Done

As you can see, the shadows service is initially stopped:

root@solaris11-1:~# svcs -a | grep shadow
disabled       18:22:13 svc:/system/filesystem/shadowd:default

So we must start it:

root@solaris11-1:~# svcadm enable svc:/system/filesystem/shadowd:default
root@solaris11-1:~# svcs -a | grep shadow
online         18:23:17 svc:/system/filesystem/shadowd:default

On the second machine (from where we want to shadow the file system), the file system must be shared using the NFS service and with the read-only attribute (ro) to avoid changing its contents during the shadowing:

root@solaris11-2:~/SFHA601# share -F nfs -o ro /solaris11-2-pool/migrated-filesystem
root@solaris11-2:~/SFHA601# share
IPC$            smb     -       Remote IPC
solaris11-2-pool_migrated-filesystem    /solaris11-2-pool/migrated-filesystem   nfs     sec=sys,ro

The advantage of using Shadow Migration is that when the data migration begins, any NFS clients that are accessing the source file system automatically migrate to accessing the target file system.

On the first machine (solaris11-1), we can confirm that solaris11-2 is offering the file system through NFS by running the following command:

root@solaris11-1:/# dfshares solaris11-2
RESOURCE                                           SERVER       ACCESS    TRANSPORT
solaris11-2:/solaris11-2-pool/migrated-filesystem  solaris11-2  -         -

Now it's time to shadow the ZFS file system from the second machine (solaris11-2) to the first one (solaris11-1) by creating a file system named rpool/shadow_test:

root@solaris11-1:/rpool# zfs create -o shadow=nfs://solaris11-2/solaris11-2-pool/migrated-filesystem rpool/shadow_test

This can be a slow process. Afterwards, you should execute the shadowstat command:

root@solaris11-1:/rpool# shadowstat
                                        EST
                                BYTES   BYTES          ELAPSED
DATASET                         XFRD    LEFT   ERRORS  TIME
rpool/shadow_test               4.73M   -      -       00:00:04
rpool/shadow_test               46.0M   -      -       00:00:14
rpool/shadow_test               52.7M   -      -       00:00:24
rpool/shadow_test               55.1M   -      -       00:00:34
rpool/shadow_test               57.5M   -      -       00:00:44
rpool/shadow_test               58.1M   -      -       00:00:54
rpool/shadow_test               59.6M   128M   -       00:01:04
rpool/shadow_test               62.8M   224M   -       00:01:14
rpool/shadow_test               89.0M   187M   -       00:01:24
rpool/shadow_test               92.7M   360M   -       00:01:34
rpool/shadow_test               120M    168M   -       00:01:44
rpool/shadow_test               163M    8E     -       00:01:54
rpool/shadow_test               178M    8E     -       00:02:04
rpool/shadow_test               178M    8E     -       00:02:14
rpool/shadow_test               178M    8E     -       00:02:24
rpool/shadow_test               178M    8E     -       00:02:34
No migrations in progress

We can verify that the migration finished by running the following command:

root@solaris11-1:/rpool# zfs get -r shadow rpool/shadow_test
NAME               PROPERTY  VALUE  SOURCE
rpool/shadow_test  shadow    none   -

Perfect! Everything worked as expected.

The same procedure could be done using two ZFS file systems. For example, we could create a new file system named rpool/filesystem_source and copy a directory that contains many files into it:

root@solaris11-1:~# cp -r NetBackup_7.5_Solaris_x86/ /rpool/filesystem_source/
root@solaris11-1:~# zfs set readonly=on rpool/filesystem_source
root@solaris11-1:~# zfs create -o shadow=file:///rpool/filesystem_source rpool/filesystem_target
root@solaris11-1:~# shadowstat
                                       EST
                               BYTES   BYTES          ELAPSED
DATASET                        XFRD    LEFT   ERRORS  TIME
rpool/filesystem_target        107K    -      -       00:00:04
rpool/filesystem_target        51.2M   -      -       00:00:14
rpool/filesystem_target        114M    -      -       00:00:24
rpool/filesystem_target        114M    -      -       00:00:34
rpool/filesystem_target        114M    -      -       00:00:44
rpool/filesystem_target        114M    -      -       00:00:54
rpool/filesystem_target        114M    8E     -       00:01:04
rpool/filesystem_target        114M    8E     -       00:01:14
rpool/filesystem_target        114M    8E     -       00:01:24
rpool/filesystem_target        672M    8E     -       00:01:34
rpool/filesystem_target        672M    8E     -       00:01:44
rpool/filesystem_target        672M    8E     -       00:01:54
rpool/filesystem_target        672M    8E     -       00:02:04
rpool/filesystem_target        672M    8E     -       00:02:14
rpool/filesystem_target        672M    8E     -       00:02:24
rpool/filesystem_target        672M    8E     -       00:02:34
No migrations in progress

Wow!!! We repeated the recipe, but we used the appropriate syntax for shadowing between two local ZFS file systems. In the same way, we're able to confirm that the shadowing operation has finished.

See Also

Here are some links to other things I've written:

And here are some Oracle Solaris 11 resources:

About the Author

Alexandre Borges is an Oracle ACE and who worked as an employee and contracted instructor at Sun Microsystems from 2001 to 2010 teaching Oracle Solaris, Oracle Solaris Cluster, Oracle Solaris security, Java EE, Sun hardware, and MySQL courses. Nowadays, he teaches classes for Symantec, Oracle partners, Hitachi, and EC-Council, and he teaches several very specialized classes about information security. In addition, he is a regular writer and columnist at Linux Magazine Brazil.

Revision 1.0, 04/09/2014

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