On Thu, Mar 31, 2016 at 3:44 PM, Grundmann, Christian <Christian.Grundmann@fabasoft.com> wrote:

Hi,

@ I'm unsure if that size should change - we've allocated blocks, they are still allocated from our perspective. From the storage point of view, there's a hole that can be used for other purposes.

I'd look on the storage side. 

 

That’s the problem, if the space is still allocated it can’t be used for other VMs so it won’t help. Is there a possibility to deallocate the free Blocks of the Disk? I think virt-sparsify would do exactly that but can’t be used with ovirt?


Well, it's tricky ;-)  - the space is allocated, in the sense that the storage 'promised' to give you X GBs of storage. It just didn't say where does blocks are going to be. So once you unmap a block, it may take it and give it to someone else. This is what thin provisioning is all about. You get logical blocks which map to physical blocks. Once those physical blocks have been deallocated, they may be used by something else, yet the logical block is still yours - and if you'll write to it, you'll get a different physical block.
Y.
 

 

Thx

Christian

 

 

 

 

 

Von: Yaniv Kaul [mailto:ykaul@redhat.com]
Gesendet: Donnerstag, 31. März 2016 14:33


An: Grundmann, Christian <Christian.Grundmann@fabasoft.com>
Cc: users@ovirt.org
Betreff: Re: [ovirt-users] Reclaim disk space of thin disks

 

On Thu, Mar 31, 2016 at 1:16 PM, Grundmann, Christian <Christian.Grundmann@fabasoft.com> wrote:

Hi,

@1. Did you use the hook?

yes, without the hook fstrim would not start,

@2. Where did you see it's the same size? Should be looked at from the storage side (assuming, btw, it supports discard!)

I looked at the “actual Size” under Storage

 

I'm unsure if that size should change - we've allocated blocks, they are still allocated from our perspective. From the storage point of view, there's a hole that can be used for other purposes.

I'd look on the storage side. 

 

I don’t know how ovirt handles FC storage and if this will allow discard.

 

It doesn't really care - thee discard should be passed to the underlying storage. Most should support UNMAP these days. But you can easily check, I assume with a small test (use sg3_utils for example).

Y.

 

 

Thx

Christian

 

 

Von: Yaniv Kaul [mailto:ykaul@redhat.com]
Gesendet: Donnerstag, 31. März 2016 12:13


An: Grundmann, Christian <Christian.Grundmann@fabasoft.com>
Cc: users@ovirt.org
Betreff: Re: [ovirt-users] Reclaim disk space of thin disks

 

 

 

On Thu, Mar 31, 2016 at 1:05 PM, Grundmann, Christian <Christian.Grundmann@fabasoft.com> wrote:

Hi,

seems not to work with FC Storage,

 

I Zero filled the Disk with dd, removed the file and did a fstrim which told me it trimmed the right amount of space,

But the disk Image stays full size.

 

1. Did you use the hook?

2. Where did you see it's the same size? Should be looked at from the storage side (assuming, btw, it supports discard!)

Y.

 

 

Thx

Christian

 

Von: Yaniv Kaul [mailto:ykaul@redhat.com]
Gesendet: Mittwoch, 30. März 2016 22:29
An: Grundmann, Christian <Christian.Grundmann@fabasoft.com>
Cc: users@ovirt.org
Betreff: Re: [ovirt-users] Reclaim disk space of thin disks

 

 

 

On Wed, Mar 30, 2016 at 10:04 AM, Grundmann, Christian <Christian.Grundmann@fabasoft.com> wrote:

Hi,

is there a way to „shrink“ a thin disk image to reclaim deleted space like using virt-sparsify?

 

Yes, if the underlying file system supports it (NFS, for example, might need to be 4.2 and above).

 

Or can it be done by making a snapshot and clone the VM to a new one?

 

Another suggestion: use the VDSM hooks for discard ('diskunmap') and run 'fstrim' from within the guest. 

Y.

 

 

Thanks a lot

Christian


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