The LUN design "question"
How many LUN, how bigger (or smaller), on how many physical disks?
You can find different post about this "problem"...
There isn't a simple answer, cause it depends on:
Storage best practice
Storage type and disks type
RAID level and number of physical disks
VM number, size and type of I/O
Max VM and I/O per LUN
Max LUN size (less than 2 TB - 512B)
Generally it's not a good idea to have very large LUNs: when you have a large number of VMs on a single VMFS based block device you will see a higher level of SCSI Reservation Conflicts which always results in performance degregation.
This occurs because the clustered VMFS LUN uses a file lock control function from the hosts and the higher the VM count the more often they have to wait on each others update housekeeping I/O activity.
See also:
SAN Configuration Guide - http://www.vmware.com/pdf/vi3_esx_san_cfg.pdf
SAN Conceptual and Design Basics - http://www.vmware.com/pdf/esx_san_cfg_technote.pdf
SAN System Design and Deployment Guide - http://www.vmware.com/pdf/vi3_san_design_deploy.pdf
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LUN size
Usually a value between 400-800GB could be reasonable.
There is also a way to calculate the size, see on this site:
Storage: How to size your LUNs? - http://www.gabesvirtualworld.com/?p=68
Here are some good threads that talk about this....
http://searchvmware.techtarget.com/tip/0,289483,sid179_gci1350469,00.html
http://malaysiavm.com/blog/best-sizing-for-single-storage-lun/
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LUN number
Usually more that one, but not too much...
It is also related by LUN size and how storage works (it works with RAID group or with a "global" RAID splitted on all disks)
Here are some good threads that talk about this....
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RAID level
