Computers and Internet

Windows Server 2012 – Storage Spaces and Data Deduplication Hands-on Review Part 2

This is the continuation of my Storage Spaces and Data Deduplication review. Here’s an index of test cases on this part and links to other parts:

  • Part 1: Introduction and Lab Environment Preparation
  • Part 2 (You’re here)
    • Physical Disk Pull
    • Introduce the Pulled Disk Back into the System
    • Extend Thinly Provisioned Virtual Disk and Observe Behavior at Limits
    • Bonus: Detecting and Replacing Physical Disk Failures
    • Removing a Disk from the Storage Pool
    • Reclaim Unused Space on Thin Provisioned Disks
    • Bonus: Defragmentation Attempt and Observations
    • Understanding Hot-Spare Behavior
    • Evaluating and Enabling Data Deduplication

 

Test Cases

Up until this point we have been provisioning the storage so we can do some tests. Starting this point I will poke at different things in the system to see how it breaks, recovers or handles the situation.

Physical Disk Pull

Note that despite my gear doesn’t support hot-swap; I’ll just pull a disk anyway… It could fail just like that in real life.

Action: 100GB disk that is part of the storage pool is physically pulled while copy activity was in progress.

  1. Answer: No apparent impact to operations. File copy continues as normal. This would have been the case with Windows Server 2008 R2 (and prior) software RAID5, so nothing new so far. Keep in mind, if this was just a “Simple” virtual disk (as opposed to parity or mirror protected), I fully expect removal action like this to bring it down along with loss of data. As we’re on parity protection here, no impact to operations observed.


Just so I show you all aspects of how Windows Server handles this “disk pull” event, here’s how Server Manager “feels” – which is not looking right at first glance. Disk 2 (100GB) is already pulled out. There is definitely some lag between the time disk pulled and the time Server Manager decides to show it. At this point I’m realizing that “Refresh” button in Server Manager is quite important. Keep reading after…


As I hit refresh button, it shows what I would expect:


Ok. Now, suppose I would like to assign one of the other drives out of “Primordial” pool. To do this, I right-click on the “Degraded” Virtual Disk, and choose “Add Physical Disk“, as in:


This brings up the following dialog. Remember, these disks are the ones showing in Primordial group (basically any unallocated disk that system can see at this point). I chose Disk4 and click OK.


Addition operation is quite fast, it shows like this almost immediately:


At the same time, disk LEDs of all physical drives in the Storage Pool went active. Presumably the new disk is getting its data generated as we have parity protection on the Virtual Disk.

At this point I’m going to attempt to remove the shadow configuration of the disk that is no longer in the system from the list of disks. Specifically the one with the exclamation mark in above dialog. Interesting observation here is going to be how long this will take. I will right-click on it and choose “Remove Disk“, like this:


Remove Disk operation on a disk that’s physically out of the system is actually quite fast. Within few seconds, I got this confirmation and a brief note as to what I should expect to happen next:


At this point I refreshed the Server Manager and everything seems back to normal/healthy, as in:


Milestone: We were able to successfully replace a failed disk without losing data.

Introduce the pulled disk back into the system

Next up is a small test about the disk that we pulled. I’d like to introduce it back to the system – but can I do that? First, remember from above steps, that I did the following:

  • Pulled it hot while running
  • Disk entry turned yellow
  • I right-clicked on it and chose “Remove Disk”
  • Server Manager refreshed and it’s no longer showing

 

Now… question is, will it come back if I just insert the disk? Such a simple looking question – you may be in for a surprise here. Keep reading.

Action: I insert the disk back in. I did this while system is running.

Drive LED came up green. Server Manager is not showing it. I refreshed the UI / no luck. So here’s the status right now (Remember, there should be total of 6 disks in the system, we’re seeing only 5). Also remember that my controller or disks do NOT support hot-swap. If you notice the “Rescan Storage” option in below dialog, I will click that. Keep reading…


Nothing happened. Still seeing only 5 disks.

Because hot-swap is not supported on this gear, I will proceed to reboot the system. Keep in mind, these disks are on a separately powered external eSATA enclosure. At this stage I have only did a soft reboot of the system. Not even power-down.

No change. Still seeing only 5 disks in Server Manager. However, when I look at the Computer Management, I see below situation. The circled disk is the one that I re-inserted and the one that’s not showing in Server Manager / Storage Spaces. Keep reading…


I did some research and asked around. I learnt the following:

  • Since I did a “remove disk” on the shadow configuration entry while the disk was physically out of the system, Storage Pool knows not to take the disk back into the pool.
  • Since the disk itself was offline during this change, it still thinks it can join the pool.
  • Because the disk in question has the remnants of the pool, it’s not showing in the primordial pool.
  • Given all of this, disk needs to be cleaned up before it can show in primordial.
  • There is still some speculation on whether the Storage Spaces / Disks view should or shouldn’t be able to show. In my case it does NOT show. Only Computer Management shows it.

 

Now let’s figure out how to do that… Right click action on the volume is all grayed out, check:


Given that all else in the GUI is grayed out, I decided to do this from diskpart. I simply issued a “clean” command on it, here:


Now I expect this to show in primordial group… and sure enough it’s there after a “Refresh”. See below.


Milestone: We were able to re-introduce the pulled this back into the system.

Continue reading additional test cases in Part 3.

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