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Storage virtualization

Posted on 2014-10-17
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We are getting Windows Server 2012 for the first time and we are looking at using Windows Storage Spaces for the first time.

We have never done virtualization and starting to learn about it. Our question is for example if you took two 500 GB drives, made them into a virtual disk and you were able to go up to a 2 TB virtual drive that is a volume and users can access it, can data be saved up to almost 2 TB on the volume?

How does the system add the other space if possible?
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Question by:regsamp
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LVL 118
ID: 40386792
Two 500GB drives, is going to give you a maximum of 1TB of space.

It's a JBOD (just a bunch of disks), so depending upon mirroring, and DeDuplication, it's unlikely you will get 2TB of data on 1TB.
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by:regsamp
ID: 40386806
Okay but we are trying to learn about virtualization and we are seeing videos of people increasing the storage size of disk drives with virtualization so ignoring the scenario above, how does the system add extra space and can you save data beyond the drive maximum? Below is a video of an example and it starts at 6:19.

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Andrew Hancock (VMware vExpert / EE MVE) earned 250 total points
ID: 40386851
DeDuplication and Compression.

Adding extra space, just add standard disks to the pool.

We currently have 10 virtual machines with virtual disk, which occupy 1.4TB in our storage pool.

Traditionally, this would take up 1.4TB of storage space.

This is deduplicated and compressed down to 348GB, and hence we have more storage available to store virtual machines. (and or standard data)
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by:regsamp
ID: 40386861
Okay, thank you.
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by:Cliff Galiher
Cliff Galiher earned 250 total points
ID: 40386876
You didn't actually post a link to a video. Storage virtualization does not change the rules of storage. You can only ever store as much data as you have physical space. To store more stuff, you either add more disks (something that storage virtualization technologies such as Storage spaces makes easier than RAID does), or you free up space through other means...such as the already mentioned dedup features. But dedup/compression is not required with storage spaces, nor does storage spaces automatically dedup. Dedup is not considered storage virtualization in any way and is an unrelated technology.

Now, again, because you didn't actually post a video link, I can only speculate on what you are seeing. But one other caveat to consider is yes, storage spaces supports a concept called "thin provisioning." This basically means I can claim to have more storage than I actually do. If you hit physical capacity, writes will still fail, even though you aren't yet at the size you claimed you have.

Think provisioning has a place in large environments and there are reasons you might deploy such a solution, but is a bad idea for most smaller organizations (which I am making an educated guess that this is for a smaller environment since most large organizations would also have virtualization experts already on staff.)
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by:regsamp
ID: 40386919
This must be a problem with the link feature then because we have tried three times now and it won't post:
https://www.youtube.com/watch?v=CxH4ADPQX6s
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Author Comment

by:regsamp
ID: 40386925
But what about this then? "This is deduplicated and compressed down to 348GB, and hence we have more storage available to store virtual machines. (and or standard data)"

"But one other caveat to consider is yes, storage spaces supports a concept called "thin provisioning." This basically means I can claim to have more storage than I actually do. If you hit physical capacity, writes will still fail, even though you aren't yet at the size you claimed you have."  

Then why would anyone want to do this??  It is at 6:19 in the video where it starts.
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LVL 118
ID: 40386952
This is not Thin Provisioning.

This is DeDuped, so if we have 10 Copies of Windows 2012 in 10 VMs, we only actually need to store the OS data on 1 VM!

hence the saving!
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by:Cliff Galiher
ID: 40386974
Actually, the video the OP linked to is about thin provisioning. The "thin or fixed" portion of the virtual disk is covered at around 8:20, not 6:19.

So yes, you can thin provision, and yes, that means you can hit a situation where your virtual disk is not yet "full" but your physical disks are. And writes will fail in this scenario.

-Cliff
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by:regsamp
ID: 40386994
The video is listed as Windows Server 2012 Storage Spaces not as thin provision and the section I was referring to does start at 6:19 and as I indicated we are trying to learn about virtulization for the first time. Stating that something will just fail and not offering help giving a new person some education in technology that is new for them is not helpful.
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by:regsamp
ID: 40386999
"This is not Thin Provisioning.

This is DeDuped, so if we have 10 Copies of Windows 2012 in 10 VMs, we only actually need to store the OS data on 1 VM!

hence the saving!"  

Thank you. We are just trying to learn more and go beyond our RAID 5 traditional setups so it seems deduplication or at least Storage Space 2012 is want we want to look more into with this Windows environment. We are a small company so this is new for us. Sorry for the confusion.
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by:Cliff Galiher
ID: 40387145
The video you linked to does *not* show dedup at all. I was giving the more specific time reference of 8:20 so that Andrew could see what you were referring to and eliminate any confusion in actually answering your question.

The video may not be labeled thin provisioning, but thin provisioning *is* a feature of Storage Spaces and the video does use thin-provisioned spaces.

As far as "saying something will fail" and not providing "help" ...I'm not sure what else you want me to do. If you thin-provision a disk (or if you follow the video guidance) and create a space that claims to have more space than the physical disks you have and then add more data than the physical disks will hold, it *will* fail. EVEN WITH DEDUP!!!  Dedup doesn't change how thin provisioning works. And dedup *DOES NOT HAPPEN IN REALTIME!*  

Sometimes the answer it "it will fail."  There is nothing to be done. There is no "help" to be provided. There is no "fix" as the system isn't broken. It is working as designed. If you choose to thin-provision and you write too much data, it will simply fail. Full stop. No change, no help, no nothing.

-Cliff
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LVL 118
ID: 40387154
No problems, I was trying to explain how you might fit "2TB in 1TB"!
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LVL 118
ID: 40387166
@Cliff My comment was about my posted comments, not the video! in response to the Authors post.

I did not see the video link posted until now!

I was going back to the how do we fit "2TB in 1TB"......DeDupe and Compression!
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by:Cliff Galiher
ID: 40387181
@Andrew: I figured, which is why I wanted to clarify. There was just a bit of miscommunication and since there was a video that, presumably, the OP may follow while setting up their environment, it is reasonable to see how they could get into an overprovisioned situation. I wanted to try and avoid that for them. I never thought you were saying otherwise in your posts, so I wanted to be very clear that the video does indeed show thin provisioning and that could be a problem if space is over-allocated, even with dedup.

-Cliff
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ID: 40387232
@Cliff

 No problems!

Andy
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