Informing the IBM Community

Removing drives from guest partitions


“You’ve not done a lot during lockdown, so it’s time to trim the fat.”

Technically words from my GP, but I figured perhaps I could apply it to my partitions as well!

To set the scene, I want to do a system save of a Power7 with the slight issue that the tape drive isn’t playing ball. It won’t handle compression for reasons that I’m still digging into, but in the meantime if I want to do the save I need to reduce my disk usage.

I have three guest partitions, each has more HDD space than they need. One solution would be to do saves of the partitions individually, so each save is smaller and I end up with four tapes. The problem with this is, in case of a DR recovery, you need to recreate the disk images and then run the restore four times.

I could make the guest partitions into virtual saves, something I talked about last year, and then save those on the primary partition. This would fit everything onto a single tape, since I’m not saving the blank space in the disk images. Again though, in a DR situation, I have to recreate the disk images before running my restore.

I want to save the disk images as well and keep everything on a single tape if possible, so let’s look at how I might be able to do that.

The simple solution would be to get rid of the excess space on the guest partitions. As of V7R1 IBM added an option in SST to allow disk removal from an ASP, this is an excellent starting point for chopping out one of the HDD images.

To avoid repeating the whole set of instructions that IBM have offered, the two main points I identified for my first partition:

  1. Currently I have 12 disk images, each approx. 37gb with about 71.5% total usage.
  2. Removing a single image will take me to 78% usage, given that the partition is static I’m not too worried about that expanding.

Screenshots below highlighting the plan and the predicted results.

After beginning the disk removal, I’d recommend finding something else to do for the next few hours. If you ever had to replace a failed HDD and sat watching the rebuild, you’re now working in reverse. The system is taking data off the drive and re-balancing it across the remaining ones, in the above example this took about 120 minutes.

You don’t have to sit and watch unless you want to, CPI09AA will be sent to QSYSOPR on completion.

Once this completes, you can verify that the drive is no longer in use by reviewing the disk configuration or checking WRKDSKSTS.

Unit 0, the artist formerly known as Unit 12 is now not used and my other drives have increased to 78% usage.

This is the first step, now I need to ditch the image and throw it in the bin if I want to save some space.

For this, power down the partition (PWRDWNSYS) and then vary off the network server description (WRKNWSD) so that you can “pull” the drive.

Once ready, you can either do this through navigator for i (if you insist then System i Navigator can do the job,) or through command line with RMVNWSSTGL.

Why would you use System i Navigator? I’ll include a screenshot of it anyway for posterity.

At this stage I’d recommend bringing the guest partition back up, just to make sure everything still works as you expect. Would hate to go ahead and delete the image and then realise you’ve unplugged the wrong one! Don’t forget to vary the NWSD back on before trying to start the partition.

Sidenote: I didn’t and you can’t prove otherwise. In theory, if you did, then ADDNWSSTGL or navigator can plug your drive back in and touch wood another IPL will get you back online!

Once you’ve confirmed that everything is as it should be then you can go ahead and delete the image. Navigator again has a task for this, or if you’re sticking to command line then DLTNWSSTG is the one you need.

A nice touch on both versions of Navigator, you can see that the delete option isn’t available until you’re removed the link to the server.

In my case I took a single 37gb image off each guest partition (3 in total) for a saving of 111gb on my primary partition or about 5.5% of its total space. Still not quite enough to squeeze everything onto a single tape, but from here I should be able to whittle down some savefiles/etc.

In theory, I could use the same process to reduce the size of a few drives (cutting another one out would take me to 85% usage which is a tad higher than I’d like.) Create a set of new 30gb rather than 37gb drives for example, add them into the ASP then slowly remove a couple of 37gb drives. I could also look at the actual data on the partition, do I “need” 60gb of PTF images on the IFS? That’s another drive and a bit there I could get rid of!

Now if you’ll excuse me, I should probably go for a walk or something before the GP yells at me again 😉

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