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Lalegre
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All Flash - Deduplication and Compression

I am having an issue where i have a really low ratio on deduplication. I already checked the proportionalCapacity to be in 0, but my ratio is still in 1.64x.

In my environment i have two different policies:

    • Erasure Coding: this one is applied on the really big machines where i have TB of space consumed.
    • Mirroring: this one is appliad to the rest of the machines.

If i have these two policies applied, will the deduplication and compression apply to both groups of VMs and between different policies?

What other factors do i have to got in mind to increase the ratio?

Thanks in advance.

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TheBobkin
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Hello Lalegre​,

"but my ratio is still in 1.64x."

I have seen worse and I have seen better in general mixed workloads (lower generally being with relatively low % capacity utilised so hard to tell).

What is your current % used of this vsanDatastore and what % of that is a few (relatively) massive VMs?

"If i have these two policies applied, will the deduplication and compression apply to both groups of VMs and between different policies?"

As it is applied at the 4K block level I don't see why RAID5/RAID1 should matter (other than potentially the parity data being uniquely unique).

"What other factors do i have to got in mind to increase the ratio?"

Many other factors:

The most important ones being the uniqueness of your data (e.g. 100% unique = zero dedupe savings, while 0% unique means +1.00x for every copy on that Disk-Group); and the size of the Disk-Groups - bigger Disk-Groups mean more data mean better odds of commonality and thus increased savings, this is obviously going to be a trade-off though as the bigger the Disk-Group the more that has to rebuild from a single disk failing, lower potential (usable) cache:capacity ratios and the fact that 2 Disk-Groups performs better than 1 (with the equivalent size cache+capacity split over 2 Disk-Groups).

More info to add to this here:

https://storagehub.vmware.com/export_to_pdf/vsan-space-efficiency-technologies

Bob

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TheBobkin
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Hello Lalegre​,

"but my ratio is still in 1.64x."

I have seen worse and I have seen better in general mixed workloads (lower generally being with relatively low % capacity utilised so hard to tell).

What is your current % used of this vsanDatastore and what % of that is a few (relatively) massive VMs?

"If i have these two policies applied, will the deduplication and compression apply to both groups of VMs and between different policies?"

As it is applied at the 4K block level I don't see why RAID5/RAID1 should matter (other than potentially the parity data being uniquely unique).

"What other factors do i have to got in mind to increase the ratio?"

Many other factors:

The most important ones being the uniqueness of your data (e.g. 100% unique = zero dedupe savings, while 0% unique means +1.00x for every copy on that Disk-Group); and the size of the Disk-Groups - bigger Disk-Groups mean more data mean better odds of commonality and thus increased savings, this is obviously going to be a trade-off though as the bigger the Disk-Group the more that has to rebuild from a single disk failing, lower potential (usable) cache:capacity ratios and the fact that 2 Disk-Groups performs better than 1 (with the equivalent size cache+capacity split over 2 Disk-Groups).

More info to add to this here:

https://storagehub.vmware.com/export_to_pdf/vsan-space-efficiency-technologies

Bob

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Lalegre
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Sorry for the delay.

The current usage of the vSAN cluster is 72% and i have a total of 153 VMs and there are more to go in the next few weeks.

Another question:

Is there a way to see if a VM is currently been deduplicated? I mean to see the information of deduplication and compression individually.

Thanks in advance.

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RickVerstegen
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Hi Lalegre​,

Another question:

Is there a way to see if a VM is currently been deduplicated? I mean to see the information of deduplication and compression individually.

No, you are not able to see this on VM level. Deduplication and compression is a cluster wide setting.

However, you can see a used capacity breakdown for certain objects. See figure below.

pastedImage_0.png

Rick

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