IO performances of the various storage provisioning

When provisioning a VM's storage, it could be thin, thick & I think there's one more type.

Q1:
What's the performance differences between them (in terms IOPS) ?

Q2:
from the guest OS (Windows or Linux), is there a way to tell what's been provisioned
is a thin, thick or ?  : assume we don't have access to vCenter to check this
sunhuxAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Q1. Thin is instant, Thick Lazy - instant, Thick Eager Zero will be more, as the VMDK is zeroed.

As difference in IOPS that would depend on your storage system.

Q2, The VM OS is unable to distinguish what the virtual machine disk provision is.
Rainer FranzelTechnical ConsultantCommented:
The main difference in terms of I/O is the following:
- with thick provisioning all the needes space of the VMDK is allocated after creation and there is no further io for allocating space in the filesystem
- thick provisioning / eager zeroed: all the space is zeroed at time of creation; no more IOs are generated during runtime of the vm
- thin provisioned: the block is allocated at the time it is written the first time.

From a performance perspective, thick provisioning (eager zeroed) is the best, but you will hardly see the difference in a normal environment. From the moment, the block is allocated and zeroed there will be no additional IOs.

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sunhuxAuthor Commented:
Thanks very much chaps.

Ok, agree the IOPS depends on the storage systems used (low-end or high-end SAN
on SATA, FC disk or SSD).

Can we have safely say thick provsng eager zero will give at least twice the IOPS of
thin provisioning on the same storage?  I've seen backup jobs run much slower
on thin provisioned VMs.

It's a pity a tenant can't find out if the cloud provider is giving them thin or thick or
thick w eager zero provisioning.  Is it common that a private cloud provider is not
obligated to reveal this information to its tenants?

What's the general practice by cloud providers?  Tenants paid for say 500GB, does
tenant get thin prov or thick prov or thick w eager zero for 500GB?  I suppose with
thin provisioning, tenants only pay actual data size (ie though 500GB allocated in
think prov, the actual data occupies 150GB, so tenant only pay 150GB?  ie pay as
per utilization?  Or even for thin prov of 500GB with 150GB actual data, tenants
still get charged the same as 500GB as if tenant is allocated 500GB thick eager
zero?)
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Rainer FranzelTechnical ConsultantCommented:
1, The number of generated IOs is not dependent on the way the underlying filesystem is structured. The IOs come from the operating system and from the applications that are hosted on this os.
What I wanted to say is that there may be ADDITIONAL IOs generated by the type of format.
The term "IOPS" is commonly used by storage-providers to show the max capability of their storage-infrastructure.

2, As a cloud provider I would not "waste" storage by not providing thin provisioned storage. But this may depend on the contract.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Cloud providers can do what they like.

Devil is in the detail of your contract.

IOPS can saturate storage and datastore just think of provisioning 1000 VMs all at once not uncommon hence why VMware is looking at Instant Clone for provisioning VMs.

1000 VMs on 20GB each would take hours to finish.

Instant Clone about 8 minutes.
David Johnson, CD, MVPOwnerCommented:
note the difference only comes into play when one is writing to the disk and the drive requests more space  Thick drives tend to be contiguous .. thin tend to be fragmented. Virtual disks are to the host nothing more than a 'file'
sunhuxAuthor Commented:
>  one is writing to the disk and the drive requests more space  
I tend to think so too esp wen there are huge logs being generated.
Though I did not do any performance tests on this, my hunch tells
me a database (esp one that auto extends) that sits in a thin prov'ed
partitioned perform conspicuously slower than a database that sits
in a thick prov'ed partition: any truth?
sunhuxAuthor Commented:
If it's thin prov, when more space is needed, there's overhead & thus some delays
involved when allocating (& sort of 'formatting') the extra new space needed, thus
this will result in slower performance: is this true?
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Correct, this is why thin disks do not perform as well as thick, and our not supported by Microsoft for Exchange.
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