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Understanding space usage of Hypervisor storage


Paul Tulloch

Question

Hi

 

I have a new instance of Hypervisor 8 running, and only a couple of VMs running on it. One is small (60GB) and the other is big (1.4TB). Each has a handful of daily snapshots. This is the storage summary:

 

image.thumb.png.4f73ae7ed3cb098b33bb48a8a627fadf.png

 

Can someone help me understand what is happening here? I didn't enable thin provisioning during installation. The figure of 3TB used doesn't even make any sense, as the combined storage doesn't exceed 1.5TB. Also, what is the 9.3TB allocated figure? Which stage do I worry about actual space issues? I have a number of other VMs to migrate to this server, and the usage (even with snapshots taken into consideration) should get nowhere near the total available space on this SR.

 

Any help much appreciated.

Paul

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6 answers to this question

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16 hours ago, Tobias Kreidl said:

Is this a thin provisioned SR, such as with NFS or local storage? You may have a number of snapshots taking up space, regardless if thick or thin provisioned.

 

Hi Tobias

 

Thanks for your reply. Thin provisioning isn't enabled, and it is local storage. There's a few snapshots, yes, but there's no way that amount of data has changed, so it doesn't make sense that it's the snapshots. I suppose I could delete the snapshots and see what happens, but if the space used returns to an expected level I'm not sure where that leaves me.

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16 hours ago, Tobias Kreidl said:

You can go to XenCenter to the storage tab and check the list of all the VDIs and their sizes on that SR and try to make sense of what you see. You can even sort the list by size.

Maybe that will help. Perhaps you have some orphaned storage instances?

 

-=Tobias

 

Hi

 

Yeah, I'd already done that. The snapshots don't have a size allocated to them, and the virtual disks total less than 1.5TB:

 

image.png.24028b143c6732b68c0b6ae453a91ed5.png

 

I can't understand where the 3TB 'used' comes from, when the above is half of that. If I delete a snapshot, the 'allocated' figure drops correspondingly. It's a concern - I can't afford for each VM's disks to take up double the amount of space they should be.

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Hi

 

In the end, I was fairly convinced that this was a thin/thick provisioning issue. With LVM, as soon as a snapshot is created the disks of the VM are duplicated, and every subsequent snapshot is then only differential. This will then lead to double the expected space used for each VM which has at least one snapshot. 

 

This was far from ideal, as I had carefully provisioned the space I thought I needed. I decided to reformat as ext3, which allows for thin provisioning. However, my main local storage volume is 22TB, and Hypervisor won't support an ext3 volume larger than 16TB! I have no choice but to use LVM, and simply not snapshot my VMs which have particularly large disks. All a bit disappointing really.

 

Anyway, hope what I've learned here helps someone else.

Paul

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