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NAS How To

Undoing The Previous NAS settings

We need to reconfigure our NAS array as a SAN array. Remember, NASes share filesystem based storage, whereas a SAN shares direct block storage. To setup SAN storage, we need to reformat our array, ripping up the XFS filesystem, and making it iSCSI.

We are going to delete our NAS volume group and create a new SAN volume group, which requires unwinding our shares and volume configuration from the bottom up.

In the Web GUI, from the Shares tab, delete the Shares entry that you created in Part 1. Then from the Volumes tab (Figure 9), delete the netarray volume, then finally delete NAS volume group using the Volume Groups right hand menu selection. I’ve seen Openfiler silently have issues with removing a volume group. So if the NAS group doesn’t disappear, you’ll need to zap it from the command line. To do this, log in as root, and at the command line execute the vgremove command:

vgremove nas

We are now back to a blank slate. Following the same procedures in Part 1 for creating a volume group, create one called san, using the same physical volume that the NAS volume group used.

Openfiler Create Volume Group

Figure 9: Openfiler Create Volume Group

Once added our SAN volume group, we need an iSCSI volume. Under the right hand menu, select Add Volume (Figure 10) and create an iSCSI volume called FiberArray. Pushing that slider over to 14 TB is so cool.

Create Volume

Figure 10: Create Volume

Done. Now to the more difficult part, configuring and bringing up the SAN services on Old Shuck.

Configuring Openfiler as FC SAN

Openfiler uses the open-source Linux SCSI target subsystem (SCST), which handles iSCSI and our QLogic HBA. To make our array available by fiber, we need to tell SCST three things: 

  • That we have an FC HBA.
  • The volume it should serve.
  • Who’s going to be asking for our hunk of storage.

Configuring these details is straightforward, but regretfully Openfiler doesn’t provide a GUI to do so. We have to do it by hand, at the shell level.

You can work from the console, or probably more conveniently, install either Putty or Cygwin and connect via ssh (secure shell). Both will let you conveniently cut and paste. By default ssh is enabled under Openfiler. Either way, log in as root.

Initially, we have some groundwork to do; we have to change when SCST will start, and enable it to run.

First, change the run level to ensure volumes are mounted and required services are up before sharing. You’ll find, the commands towards the top of SCST initialization script, in /etc/init.d, a chkconfig directive. Doing a grep chkconfig /etc/init.d/scst should bring you to where you need to be. It should look something like this:

[root@OldShuck ~]# grep chkconfig /etc/init.d/scst
#chkconfig: — 14 87

Using your favorite editor, change the first number, in this case 14, to 99. This will move the startup of the scst service to the end of the line, ensuring everything it needs has already been started. If you grep the file again, it should now read:

#chkconfig: — 99 87

We can now tell Old Shuck that it needs to start the scst service at boot-up, and we’ll go ahead and start the service now so it can be configured.

This should look like:

[root@OldShuck ~]# chkconfig scst on
[root@OldShuck ~]# service scst start
Loading and configuring the mid-level SCSI target SCST.
[root@OldShuck ~]#

One last thing, we need the name of the demon if we are to summon him. In this case, that name is the unique identifier for your HBA. The WWN is in a file called port_name, in a directory assigned by the system. To get it:

cat  /sys/class/fc_host/host*/port_name

Navigating directories, it looks like this:

[root@OldShuck ~]# cd /sys/class/fc_host
[root@OldShuck ~]# ls
host5
[root@OldShuck ~]# cd host5
[root@OldShuck ~]# cat port_name
0x210000e08b9d63ae

When working with your WWN it is parsed like a MAC address, by hex byte, so Old Shuck’s WWN is 21:00:00:e0:8b:9d:63:ae

We have everything set up and are now ready to start configuring SCST. SCST is configured through the scstadmin command, we will use scstadmin to set scst parameters, then write the configuration to /etc/scst.conf so it persists across reboots.

First, to enable FC HBA as a target host, you’ll need the WWN from above, i.e. scstadmin  -enable  <your wwn>

[root@OldShuck ~]# scstadmin –enable 21:00:00:e0:8b:9d:63:ae
Collecting current configuration: done.
—> Enabling target mode for SCST host '0x210000e08b9d63ae'.
All done.
[root@OldShuck ~]#

Now add the array to SCST. We’ll assign the array a device name, tell it to use the virtual disk handler, provide the device path to the volume we set up above, and, for now, use the WRITE_THROUGH cache policy, i.e. scstadmin –adddev  <your device name> -handler vdisk   -path /dev/<volume group>/<volume> -option WRITE_THROUGH

[root@OldShuck ~]# ls /dev/san
fiberarray
[root@OldShuck ~]# scstadmin —adddev SAN_LUN0 —handler vdisk —path 
/dev/san/fiberarray —options WRITE_THROUGH
Collecting current configuration: done.    —> Opening virtual device 'SAN_LUNO' at path '/dev/san/fiberarray' using handier 'vdisk'.. All done

The WRITE_THROUGH option means that we acknowledge the write once it is flushed from the cache to the disk. We could use WRITE_BACK policy option, which acks the write before it is flushed, problem is, if the power fails or something else goes wrong you could lose data. The tradeoff is speed, it takes time to flush the cache.

We now assign our device to the default group and give it a LUN. SCST provides for groups to ease administration of who can access what. SCST comes with a Default group (note the capital D) which is just that. We’ll assign our device to that group and give it unique logical number (LUN), in our case, zero, i.e. scstadmin –assigndev  <your device name>  -group Default –lun  0

[root@OldShuck ~]# scstadmin –assigndev SAN_LUN0 —group Default —lun 0
Collecting current configuration: done.
    —> Assign virtual device 'SAN_LUNO' to group 'Default' at LUN '0'..
All done.
[root@OldShuck ~]#

If you were to have multiple volumes, you’d increment the LUN for each subsequent volume.

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