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Does the 3par de-allocate space from a thin-provisioned VLUN?

StuartA46
Frequent Advisor

Does the 3par de-allocate space from a thin-provisioned VLUN?

We have HP 3PARs with Linux, W2K12 and VMware ESX 5.X servers.  Does the 3PAR "de-allocate" storage space from already provisioned VLUNs?  i.e. if a user on a Linux server writes 100 GB to a file, then removes the last 50 GB, does the 3PAR get the message and release the last 50 GB?  What about "random" I/O, as from Oracle?  If an already-populated Oracle Database releases old records in random locations around the DB, will the 3PAR release "chunks" of the DB space?

3 REPLIES
Sheldon Smith
Honored Contributor

Re: Does the 3par de-allocate space from a thin-provisioned VLUN?

It pretty much depends on the operating system. The OS has to tell the 3PAR the space is now available. Either using an "UNMAP" function or by overwriting the storage with zeros.

 

See section "Reclaiming unused space" in the HP 3PAR Thin Technologies whitepaper # 4AA3-8987ENW, dated Feb 2015.


Note: While I work for Hewlett Packard Enterprise, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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Mark Smithers
Regular Advisor

Re: Does the 3par de-allocate space from a thin-provisioned VLUN?

As already mentioned it all depends on the OS.  However, there are some further things to bear in mind and I hope I have the facts correct here.

 

1) You have to "zeroise" the free space - SDELETE for example on a Windows server

 

2) In order to release space, you have to make sure it is CONTIGUOUS space you are removing.  By this the 3par detects if it is more than 128MB before releasing the space back to the CPG pool.

 

2a) Windows 2012 has a shockingly bad defrag tool! Use something else to defrag the free space

 

3) When deallocating the space, it retains 1GB of space per controller per pairr that the presented storage uses. i.e. 2Gb, 4GB, 6GB or 8GB

 

4) When you have fought the good fight and it releases space, don't forget to tune your CPG to release the space back to the system overall or it will stay in the CPG until it is needed again.

 

So, yeah, I hope the numbers are correct above, the principles are OK I think though.

 

Cheers

Mark

 

Sheldon Smith
Honored Contributor

Re: Does the 3par de-allocate space from a thin-provisioned VLUN?

That's why I wrote, "get a copy of whitepaper 4AA3-8987ENW". (Google is your friend.)

 

For example, Windows 2012 can be smart enough to UNMAP deleted storage as it goes so you don't have to zeroize the freed space. As can some other OS file systems. 


Note: While I work for Hewlett Packard Enterprise, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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