Eager Zero and Lazy Zero in Vmware

Can someone clarify the meaning of Eager zero and Lazy zero in vmware ?
If I understand if you create a VM and select the disk as Thick and assign it 500GB, then even if you happen to write 100GB data on the VM vmdk file, it still counts as 500GB on the storage.
if the storage runs low in space, other VMs cannot use the 400GB left for your VM

if you select thin, and assign it 500GB , but you write 100GB to the vmdk , then it will count as 100GB on the storage.
if the storage space is running low, other VMs can use whatever you have left from 500GB , example the 400 GB

If I am not wrong Thin disk does not user eager zero and lazy zero

Any clarification ?

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JohnBusiness Consultant (Owner)Commented:
You can allocate a total amount of disk but not pre-assign or pre-allocate it, and so the VMDK will use as much disk as it needs and expand to the maximum.

If you allocate it all at the beginning, then all the space is used and no other application can use the space.

This is normal VMware behaviour.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
eager zero and lazy zero, is when the Hypervisor, clears all the sectors/blocks on the virtual disk, with zeros, this makes the performance of an eager zero disk slightly faster in tests, than a lazy zero, which is done before data is written to the disk.

When you create an eager zeroed disk, it takes longer, as all the sectors are zeroed, lazy zero, they are done of the fly.
jskfanAuthor Commented:
Eager zero and Lazy zero if I am not wrong they work only with Thick disk.
When should I worry if I need to select eager zero or lazy zero

does zeroing mean formatting ?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
It's not formatting, but zero-ing out the data on the block.

if you need to use Fault Tolerance, or fast performing virtual disks!

Thin are naturally, lazy zeroed.

see here


jskfanAuthor Commented:
Sorry Guys, was very busy and could not get back with you sooner:

Well speaking Thick Lazy Zero, why would we go with it at the first place ?
Since the disk block has to be zeroed out before the data is written to. Means Low performance
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I would not say low performance, have to tested it and compare the difference ?

It was the default thick setting!

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jskfanAuthor Commented:
Thank you Guys..I will come back to this topic later,
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