Thin LUN "Consumed Capacity" shows unaccurate info

AFAIK capacity that is once used cannot be taken back, so if a block is written, space is consumed on the thin LUN. If you delete the data from dat block, the Clariion doesn't know that, it only sees blocks that the host has once written to. If you overwrite old block, nothing changes, if you write to new blocks, more capacity is used.

This is exactly what is happening. Does not make any sense to me.

If Clariion knows when a server needs a new block, why does not know about a deletion? It's probably a design issue.

The whole idea of Virtual Provisioning is to buy time oversubscribing. But you don't want to reach a point where you will be out of space, so, you need to manage "consume capacity".

My question now is how can I manage the real consumed space? I guess I can not.

Thanks a bunch for your answer,

Pablo

Pablo,

i do not know if this functionality is available in Windows 2003 but it Windows 2008 you can shrink LUN size in the OS using VDS ..and then it should allow you to shrink LUN size in Clariion. Take a look at this paper

https://powerlink.emc.com/nsepn/webapps/btg548664833igtcuup4826/km/live1/en_US/Offering_Technical/Technical_Documentation/300-007-439_a05.pdf

ah yes ..no support for shrinking thin LUNs. Bummer

Aran,

according to this you can shrink LUN size in Clariion

emc230411

Yeah,

I can see what you are saying. What a shame anyway.

What Dyname ad you are saying makes perfect sense now.

Thanks,

Pablo

Correct me if I am missing the point, but is that necessarily what is trying to be accomplished here? We are talking about the consumed capacity of a thin provisioned LUN not the size of the LUN that was provisioned right? If the thin LUN is 100GB, the application consumed 20GB then 10GB of data was deleted, the consumed capacity is still 20GB. Shrinking the LUN would be going from a 100GB thin provisioning to 50GB or 20GB provisioned LUN. So to recclaim that 10GB of space from the deleted application data you would have to shrink the 100GB LUN to 10GB, then expand it again so that the application can grow.

i was thinking of the ability to shrink the consumed space.  If NTFS volume grew to 20G, you deleted 10G worth of data ..now shrink the NTFS volume and lun to 12G ..thus releasing 8G back into the pool. Am i completly off here ?

Message was edited by: dynamox

But in the example I used the NTFS volume is 100GB, not 20GB. That is the consumed space. The command you are referring to shrinks the LUN and the NTFS volume. So if you shrink it to 12GB after 10GB was consumed, you will then need to expand the LUN size if more than 12GB is needed and then use dispart extend command to extend the size of the LUN and NTFS volume. And to expand the volume on the array we are still limited to LUN migration or metaLUN right?

Pablo,

The process is not that simple and I don't think that the tools currently exist to make this an easy process. Shrinking the LUN is one process, and if you read the primus article is only supported on Windows 2008. But as you have pointed out, to reclaim space you would need to shrink the LUN to the size of the data used on the LUN and then use migration tools to migrate the LUN to a larger size in order to expand the LUN.

This sounds like a lot of work to me and I don't see it as being that right way to go about this.

See, that is where I would do it differently. I would charge them for what was provisioned not consumed

Dynamox,

I'm not a Windows expert.

if you deleted 10 GB worth of data, how you shrink the volume? And if you shrink the volume? How you expand it again?

Lets say I have a 100 GB Thin LUN.

On windows we format a 100 GB  drive.

The file system grew to 20 GBs and then back to 10 GB.

Are you saying you will reduce the size of the drive to 10 GB and then to 100GB again? That will release the "unused" space?

I'm not sure if I followed you.

Thanks,

pablo

ahh.. i see your point.  You could expand by using PowerPath migrator to new (bigger LUN). I know it gets convoluted but i was thinking of a scenario where i give a thin provisioned 100G LUN to a database server, they have a process that goes crazy that actually writes 90G worth of garbage to this LUN.  They delete garbage data  and now they don't want to pay for consumed space , only for space they actually use.