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Useless1
Contributor
Contributor

PS5000E Thin Provisioning?!

Hi,

We have a PS5000E in a ESX 3.5 farm. I am new to this SAN device and am trying to understand how thin provisioning works?

I understand as we are in ESX 3.5 using ISCSI VMware itself is not doing any thin provisioning, however it appears the PS5000E unit is... (As in I can create several disks in VMware of say 100GB and put a few GB's of data on them, but in the PS5000E console it shows only the few GB's actually being used.

The thing I do not understand is VM Aware Storage (VMAS), and vStorage etc etc...

I take it with this current setup, if I were to storage migrate a host from one LUN to another, the used space would remain the same on the old LUN (As in it would not free up after the move) because the Equallogic's idea of thin provisioning is based on the physical storage simply being accessed?

We are looking to upgrade this farm to vSphere 4 which would allow Thin Disk's via the GUI etc, so we could have double Thin Provisioning going on... and I keep reading about something in VMware which would allow it to talk to the SAN to tell it if a storage migration takes place to free up the physical space used on the old LUN... (Is this vStorage and since when has this been available) and how do I find newer products with this functionality?

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curriertech
Enthusiast
Enthusiast

That is quite strange! So if you create a 200G disk file on the datastore, the EQL volume shows significantly lower utilization? In my experience this would be normal at the point of creating the datastore as it is just a container and not a flat file like a .vdmk, but as soon as I add a vdisk at x size, that x size is reflected on the EQL side. I'm down to one ESX3.5 host and it's not connected to my EQL box, but I'll hook it up and test this next week to see if I can duplicate this behavior.

A comment on thin provisioning in ESX4 - it does have an impact on performance but only when enough data is added to grow the disk file, as it writes out the new disk blocks before it writes the data. For application servers that don't have much change in data volume this is just fine, but on servers prone to regular data growth I would stick with thick provisioned disks.

-Josh.

-Josh.
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jbogardus
Hot Shot
Hot Shot

With storage system (EqualLogic, NetApp, ...) Thin Provisioning the storage system only uses space when data is actually written to the space (block) the first time. As long as no data has been written to the block of storage the storage logic will simply virtual present that empty block as being available to write to but will not actually allocate a physical block on disk to store the data but rather just keep track of the virtual bock being empty. Once data is written to the block for the first time the storage system can no longer assume that it is empty, even if the application later deletes data from the disk, so a physical block get permanently allocated for that block of the LUN until the LUN is deleted.

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curriertech
Enthusiast
Enthusiast

Yes but unless thin provisioning at the .vdmk level is being used, the .vdmk being a flat file should take up its respective size on the EQL volume, no?

-Josh.

-Josh.
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AndreTheGiant
Immortal
Immortal

Yes but unless thin provisioning at the .vdmk level is being used, the .vdmk being a flat file should take up its respective size on the EQL volume, no?

True, but only if you use eagerzeroedthick format (not the default one).

If you use the default (zeroedthick) the space on storage will grow "on demand".

Andre

Andrew | http://about.me/amauro | http://vinfrastructure.it/ | @Andrea_Mauro
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awliste
Enthusiast
Enthusiast

only two ways a vmdk flat will take up the entirety of its size: zeroedthick and eagerzeroedthick, and only one of those truly takes up the whole.

Zeroedthick - given, say, 500 GB with 100 actually used, will have the remaining 400 defined in its vmdk, but not pre-zeroed out. That 'space' is striped, and consumed on demand. Eagerzeroedthick has the whole enchilada - all 500 GB - zeroed out and ready to rock and roll. FWIW, be cautious with some aspects of vStorage motion and vmdk's with this: you can go from thin to eagerzeroedthick, but not zeroedthick, and even then only when you change datastores. If you try the vStorage wizard on a disk in the same datastore, it will act and indicate as if it was a successful task, but there will be no change. To affect a disk type change to a vmdk resident to the same datastore, you must use 'inflate' on the vmdk.

Good luck trooper.

- abe

Integritas! Abe Lister Just some guy that loves to virtualize ============================== Ain't gonna lie. I like points. If what I'm saying is something useful to you, consider sliding me some points for it!
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curriertech
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Enthusiast

Thanks for the clarification Abe and Andre!

-Josh.

-Josh.
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