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Sizing LUN & raid array in ESX 3

I've read a lot of threads on this subject and here are the decisions I've taken for our production environment. Comments are appreciated Smiley Happy

We'll be running everything across 7 hosts connected by FC to an NSC55.

number of VMs to convert : 54

total size : about 3 Tb

physical disk : 300 Go @ 15K RPM

RAID-5 (3+1) for a total of about 850 Gb by array (usable)

2 * 425 Gb LUN by RAID array

1 datastore = 1 LUN

we plan to always keep between 50-100 Gb of available disk space in a datastore.

all the drives in a VM (C, D, E) will be stored inside the same datastore for ease of management

combined I/O for the 54 VMs is about 350/sec with burst in the range of 1100.

since this is only the first step of our migration, we took the less used servers in our farm hence the RAID-5 decision.

All the VMs will have sufficient RAM allowed to eliminate swapping.

All the VMs runs Windows Server 2003

So, how's that ? What about SCSI locks (reservations) ?

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So each VMFS datastore/LUN will have about 27 VMs? I think that's a little higher than perceived wisdom suggests (i.e. 10-15 VMs per LUN, to avoid SCSI reservation issues)....what about more smaller LUNs?

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Since we have about 3 Tb of data, we'll have at least 4 RAID array (8 LUNs)

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SCSI Reservation requests or locks happen anytime the metadata of the VMFS is modified. This can be due to changing the access, modification, and create times; permissions; location; size of a file on a VMFS. Pretty much touch a file on the VMFS and you have a reservation request. When there are too many for the SAN to handle you get a conflict. 20 such conflicts in a row and you have failure. It is therefore urged that you present smaller LUNs and more of them to minimize impacts of reservations. Generally 1/2 TB LUNs work better than full TB luns but this depends on the size of your VMs. YOu may have large disk VMs and therefore an RDM may be best.

The size of your LUNs, placement of the VMs, whether to use RDMS or not depends solely on the application in use on the VMs and the current disk requirements.

Best regards,

Edward L. Haletky, author of the forthcoming 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', publishing January 2008, (c) 2008 Pearson Education. Available on Rough Cuts at http://safari.informit.com/9780132302074

Edward L. Haletky
vExpert XIV: 2009-2023,
VMTN Community Moderator
vSphere Upgrade Saga: https://www.astroarch.com/blogs
GitHub Repo: https://github.com/Texiwill

Here is some information that might help determine space requirements

per VM.

The space requirements for a single VM are the total of the following:

+ 1 MB for the configuration files

+ Size of the virtual disk(s)

+ Size of the configured memory (minus the reserved memory) for the .vswp file

+ Size of the configured memory for suspending the VM

+ 100 MB for log files

+ An undetermined amount of space if using snapshots and storing them locally