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cDOT and Vol Move

Posted by lwei in Pseudo Benchmark on Aug 16, 2013 2:43:21 PM

On clustered Data ONTAP (cDOT), you can do volume move (vol move) not only from one aggregate to another within a node, but also from an aggregate inside node1 to a destination aggregate inside node2. That is to say, you can do vol move across the node boundary; and do so non-disruptively.


Below, I’ll use a very simple example to illustrate how this can be done.


Let’s say we have a two-node cluster, running version 8.2, with aggr3 inside node1 and aggr4 inside node2 (see Figure 1). Both aggr3 and aggr4 are 64-bit aggregates. We also have a Vserver, myVserver, which uses aggr3 and aggr4 (see Figure 2). If you need to know the details of how this step is done, please follow the link here.

blog_2013aug16_fig1.png

     Figure 1. Two aggregates: aggr3 in node1 and aggr4 in node2.

 

blog_2013aug16_fig2.png

     Figure 2. A vserver: myVserver, uses both aggr3 and aggr4.

 

Next, let’s create a 10GB FlexVol volume, vol_10g, on aggr3 and create a 8GB LUN, my8GB.lun, inside vol_10g. We then map the LUN to a Windows host, in this case, stlrx300s6-187, via an iSCSI LIF (see Figure 3). Note, the detail steps of how to create an iSCSI LIF can be found here.

blog_2013aug16_fig3.png

     Figure 3. The mapping of the 8GB LUN inside vol_10g.

 

Now, on the Windows host, we format the 8GB LUN and assign a drive letter Y: to it (see Figure 4). In order to demonstrate the non-disruptive aspect of the vol move operation, let’s run Iometer while doing vol move. In our case, the Iometer test file is 5GB in size. The IO pattern is 70% read, 30% write, 100% random. And IO transfer size is 8K. One more thing, let’s use perfmon to monitor the whole process. And we are ready to go.

blog_2013aug16_fig4.png

     Figure 4. The formatting of the 8GB LUN.


First, we start Iometer and let it run for a couple of minutes. Then, we initiate the vol move process (see Figure 5). In this case, we move vol_10g from aggr3 inside node1 to aggr4 inside node2.

blog_2013aug16_fig5.png

     Figure 5. The vol move operation.


Figure 6 is a perfmon log chart that captures the entire 10-minute Iometer run. It shows that Iometer was running before vol move had been started, and kept running during and after the vol move operation.

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     Figure 6. The perfmon log showing the 10-min Iometer run and the 2-min vol move.


The vol move operation took about two minutes to complete, from 9:06:42 PM to 9:08:42 PM. Figure 7 shows a zoom-in view of how Iometer was running during the vol move process. Note that there is a brief period (about 10 seconds) where there was no IO. This is expected, because there is a brief IO “freeze” during the vol move process in order to transfer the identity of the source volume to the destination volume. 

blog_2013aug16_fig7.png

     Figure 7. The zoom-in view of Iometer running during the vol move operation.


Figure 8 shows the final status (successful) of the vol move operation, together with the destination where vol_10g ended up with, that is, aggr4 in node2.

blog_2013aug16_fig8.png

     Figure 8. The final status of the vol move operation.

 

 

Thanks for reading.


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