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cforest
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ESXi 6.0 with HDD RAID 5 and a separate SSD disk: where to install ESXi itself

Hi there,

I have a DELL PowerEdge R630 server with the following disks:

1. HDD RAID 5 built from three HDD disks 1 TB each (in total, it provides 1.9 TB)

2. A separate SSD disk (900 GB)

There going to be lots of machines on this server, and for some of them, I would like to provide the highest performance. With this goal in mind:

1. Does it make sense to install ESXi on a SSD disk, or I'd better install it on HDD RAID 5?

2. Does it make sense to place on SSD those virtual machines from which I have the highest performance?

For p.2, I think it makes sense, but I am not that sure about p.1. Or, maybe I wrong for p.2, as well?

Thanks,

cforest

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MBreidenbach0
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ESXi loads into RAM and then runs from RAM. Later it just writes config data back to boot media from time to time and when it shuts down. So - the type of boot media will just affect ESXi boot time. But not much.

(Since it can PxE network boot you don't need a local boot media at all.)

VMs on SSD of course usually are faster than VMs on hard drive RAID 5 (that stuff always depends on the workload i.e. what the VM actually is doing regarding read/write IO)

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MBreidenbach0
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SSDs can fail - so a single SSD may not satisfy your availability requirements.

Can Dell RAID controllers use SSDs as cache ?

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cforest
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MBreidenbach0, thanks for the answer.

Honestly, I have no idea if Dell RAID controllers can do it.

As to installing ESXi on SSD disk, will I get performance increase in comparison with ESXi installation on HDD RAID 5, or virtual machine performance depends on where the virtual machine itself is installed (SSD or HDD), not the ESXi operating system itself?

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MBreidenbach0
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ESXi loads into RAM and then runs from RAM. Later it just writes config data back to boot media from time to time and when it shuts down. So - the type of boot media will just affect ESXi boot time. But not much.

(Since it can PxE network boot you don't need a local boot media at all.)

VMs on SSD of course usually are faster than VMs on hard drive RAID 5 (that stuff always depends on the workload i.e. what the VM actually is doing regarding read/write IO)

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cforest
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Thank you!

One more related question, if possible. In regards of the performance of virtual machines located at SSD drive: is it important that ESXi determines my SSD disk as non-SSD? Will it affect virtual machine performance? Should I do something like described in this article: VMware Knowledge Base Or, it just doesn't make sense in the context of my goal (better performance of virtual machines located at SSD)?

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MBreidenbach0
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ESXi can do some special stuff with SSD drives if it 'knows' its SSD (like swap to SSD). And there are scenarios where you have a RAID controller but don't use that feature so you configure each drive as separate RAID0 logical drive - sounds stupid but is required i.e. in some VSAN scenarios. Here ESXi usually won't recognize SSD drives as SSD. But they can be marked as SSD drives so for example VSAN can use them as cache drives.

VM IO performance should be the same whether ESXi 'knows' its SSD or not.

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cforest
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MBreidenbach0, thank you!

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