Sienahk
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VxRail: Storage Usable capacity

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Dear All,

Base on reading from previous discussion, the usable space is about 48% of the RAW HD size (excl. SSD for caching purpose)

However the sizer doesn't tell the actual usable capacity.

For the first VxRail, the following VM are also needed and will take up extra  space from the VxRail cluster.

I am wonder if the optional parts: RP fro VM, CloudArray and VDP, can be ignored if customer is not intended to use them?

Or such VM cannot  (or should not ) be deleted from the VxRail cluster?

Space.jpg

Thanks,

Donald

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RichardPreston
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Re: VxRail: Storage Usable capacity

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Hi Donald,

The VMs for VDP and RPVM (and ESRS and CloudArray for that matter) are only deployed in a VxRail cluster if the customer explicitly installs those services. If those services aren't installed, then the values in the table you reference in your post can be ignored.

Richard

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RichardPreston
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Re: VxRail: Storage Usable capacity

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Hi Donald,

The VMs for VDP and RPVM (and ESRS and CloudArray for that matter) are only deployed in a VxRail cluster if the customer explicitly installs those services. If those services aren't installed, then the values in the table you reference in your post can be ignored.

Richard

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Jaideep13
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Re: VxRail: Storage Usable capacity

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So What would be a good estimate to provide customers with when asked the question "How much usable capacity can I expect from a VxRail Appliance?"

Also, I remember someone mentioning that the FTT setting on a hybrid appliance is set to 1 by default and cannot be changed. Is this true or can the customer specify the FTT setting per VM and choose between FTT=0,1,2 and 3?

Thanks.

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RichardPreston
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Re: VxRail: Storage Usable capacity

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I'll answer the easy question first. FTT value can be set per VMDK in VSAN on all VxRail models (the all-flash models also offer EC-1 and EC-2 as choices).

The quick, unqualified answer to how much usable capacity can I expect with VxRail is "up to nearly 50% of raw capacity" for hybrid systems and "up to nearly 75% of raw capacity" for all-flash systems.

In order to provide a more accurate answer, you need to understand your customer's workload:

What FTT or EC value?

How much of the allocated storage actually be utilized on average?

How many IOPS?

FFT and EC value obviously have a huge effect on usable capacity.

The latter two questions pertain to the amount of slack space (headroom) that's required. VMware has a best practice for VSAN to leave 30% of the formatted capacity (before FTT) unused as slack space. That slack space is intended to prevent any capacity drive from exceeding 80% utilization. When that happens, VSAN automatically rebalances the datastore, and that can consume 15-20% of the available IOPS. You cannot turn off this automatic rebalancing, but you may be able to reduce the chance that it happens by regularly manually invoking a rebalance in off-hours.

In my opinion, 30% slack space is overly conservative, as it's only really an issue if the rebalance occurs while the VxRail cluster is running over 80% of its performance capacity. If VxRail is running at less than 80% of its performance capacity, then 15-20% fewer IOPS being available for the workload shouldn't affect the performance of a workload.

Furthermore, since VSAN by default thin-provisions storage allocated to VMs, and by default doesn't allow storage over-subscription, it's unlikely an automatic rebalance will occur if the VMs actually utilize on average less than ~75% of their allocated storage. I believe it's fairly common for storage utilization to be significantly lower than storage allocation, especially for VDI.

I hope this helps.

Richard

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Jaideep13
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Re: VxRail: Storage Usable capacity

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This is incredibly useful! Thanks a lot Richard!

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