How much space to leave on a datastore, ESXi 5.1?

Hello Experts,

      My question centers around how much space to leave on a datastore. I am running ESXi 5.1.  I have one datastore that has 832GB of space running on a RAID 10 volume. That volume is created using 6 300GB 15k drives. It is the only datastore available. On this host I hope to have four VMs running server 2012. One VM will be a SQL/Web server using approximately 400GB. Two VMs will be application servers using 100GB each. All three of these servers combine to make one running application. The last fourth server is a Test server for the application using approximately 200GB. That is 800GB of the datastore leaving only 32GB left.

      I don't plan to use the Snap shot feature or VMotion and the servers will be backed up to another location using Trilead. I chose the RAID 10 setup for the read / write increase but could get another 500GB using RAID 5 losing the boost in write speed. I would really appreciate the opinions on this. As an option I could take the Test server off this host and move it into another host freeing up 200GB but want to hear what people think first.

Thanks You, Gary
xrayeyesAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)Connect With a Mentor VMware and Virtualization ConsultantCommented:
With low numbers of VMs - 15%

but be careful, if backups, with snapshots (and watch those snapshots!).

Also, performance loss with RAID 5, compares to RAID 10.
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James HIT DirectorCommented:
Gary,

You have to consider vswap space as well.  How much RAM does this server have and how much are you giving the VM's? I don't think it is in your best interest to leave so little space left. You run out of space and your VM's stop functioning. I don't think you want to deal with that so it would be best to move that test server elsewhere.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
We like to leave at least 20%-25% free on the datastore, this is dependant on the number of VMs per datastore.

(this figure has been based on experience of using VMware vSphere for over 16 years!)

This is based on backups using snapshots, and also remember that VMs when powered on also create a SWAP file equal to memory in the VM.
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xrayeyesAuthor Commented:
Spartan,

Total RAM on host is 24GB. Server 1 8GB memory, Server 2,3,and 4 4GB of memory for a total of 20GB used by VMs leaving 4GB for Host. ESXi is running off dual SD cards in Dell R820rserver.

Andrew Hancock,

That is the number I was looking for, 20 to 25%. So losing the 4th test server may be the option allowing me to have the 25% and still keep the RAID10. Or nuking the RAID 10 (832GB) and going with RAID 5 (1.4TB) which allows me to keep everything on this one host.

I am going to leave the question open for a day or two to see what other types of answers I get back. Thank you to both of you for responding so quickly.

Thanks, Gary
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James HConnect With a Mentor IT DirectorCommented:
You are too close to the limit with the RAM.
If you need the performance, then stick with RAID 10 but I would definitely remove the test server.
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xrayeyesAuthor Commented:
Thank you Spartan_1337 and Andrew Hancock! Although Andrew's answer went straight to the point of 20-25% should be left free on the datastore I ended up using both of your comments/advice in making my decision. I am moving the Test Server to a different host. That will give me the 25% free space on a RAID 10 volume and plenty of Ram for the host to use. I would rather have the space and memory there for the unforeseen later.

Thanks again, Gary
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