Comments on: Performance of Thin Provisioned Disks

By: Scott

Scott — Wed, 20 Jan 2010 14:34:29 +0000

vmkfstools in the console will allow you to convert disks of any format to any other. But note that the default format is lazy zeroed thick. Unless you have changed that, no conversion should be needed.

By: Peter

Peter — Wed, 20 Jan 2010 09:46:16 +0000

Is there any way to convert an eagerzeroedthick or a thin disk to the lazyzeroedthick format or is this only possible by creating new disks?
I want to only use the thin capabilities of our array.

By: AQU

AQU — Wed, 06 Jan 2010 08:03:00 +0000

Aha okay, I get the point, tnx man.

By: Scott

Scott — Tue, 05 Jan 2010 17:33:28 +0000

AQU,

No, the zeroing of a “previously zeroed” (zeroed in metadata only) block will not be less than a new, unzeroed block. In both cases a full 1MB of zeroes must be written to disk. In the second case a small amount of metadata must be updated. But that write is very, very small with respect to the zero block.

Scott

By: AQU

AQU — Tue, 05 Jan 2010 07:51:27 +0000

Makes sense, tnx for the info Scott. Clears a lot of clouds.

Now taking it to a next step, when talking in terms I/O time,
I presume that run-time zeroing of a new “previously zeroed” block will be lesser then to a new “non zeroed” block, as the latter actually contains data which needs to be cleared/formatted, thus will take more time writing to.

By: Scott

Scott — Mon, 04 Jan 2010 19:06:00 +0000

VMFS records zeroed blocks for thin provisioned disks in metadata only. This means that when you convert an eager zeroed thick disk to a thin disk the zero blocks will not be represented on disk. That space will therefore be reclaimed.

Once the guest OS writes non-zero data to the logical block then a new block will be created and the thin disk will grow.

By: AQU

AQU — Fri, 25 Dec 2009 12:50:25 +0000

Thanks Scott, really appreciate it.

Enjoy the holidays!!

By: Scott

Scott — Fri, 25 Dec 2009 00:41:16 +0000

Good question, AQU. You have stumped me. I am going to have to run down an answer for you with engineering. Unfortunately it may take until after the holidays (4 JAN 09) before I can get an answer. But I am on it!

By: AQU

AQU — Thu, 24 Dec 2009 12:39:06 +0000

We are in the process of converting thick zeroed disks (tbz=0) to thin disks. The LUN’s are on an HP EVA.

How does this effect the disk when it will start to grow dynamically?
Will it do the zeroing again?

With other words: Will the already zeroed space on the LUN be lost during conversion? Or will the vSphere host be able to recognize that the space was already zeroed before the conversion?

By: Virtualization Short Take #32 - blog.scottlowe.org - The weblog of an IT pro specializing in virtualization, storage, and servers

Wed, 23 Dec 2009 04:14:54 +0000

[...] Drummonds posted a good article with a performance comparison of thick provisioned disks vs. thin provisioned disks. This is good information and helps to clear [...]