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LUN Carving?

We are in the process of a SAN/VMWARE purchase and i have a couple questions for the experts.  When configuring LUN's on a SAN is there any advantage to making smaller LUN's out of all the spcae or is it better to create one big LUN?  I understand that using seperate LUN's fro different drive types (SAS and SATA) but was curious if i had a 2TB (all SAS drives) LUN is that better than 2 1TB LUN's?  Is there a performance difference at all?  

Related to SAN's adn VMWARE - I know some of the SAN's come with the software that have snapshot capabilities and some are limited to how many snapshots.  My question is, Will limited snapshots be a big issue if we are running VMWARE Infrastructure 3.5?  There is snapshot capabilities with VMWARE also if i'm not mistaken.  Any help on this is always appreciated.  Thanks!!!

Perry
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Lonewolf70
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There are lots of factors that will contribute to what is the "sweet spot" for LUN sizes for your VMware environment.  What I have heard the most from VMware guys regarding your question is that they always recommend using more, smaller LUNs than one larger LUN.  The reason that they give is usually that they are afraid a very large LUN will be wrapping around and hitting the same spindles over and over again and performance will be impacted (for example, if you were to create one very large LUN out of a single RAID group).  If you can ensure that your LUN is spread across as many physical spindles as possible, you should be fine with going with at least 1TB.  Be careful with going too large also.  I think that the largest supported LUN size in 2.5 was 2TB, but I think it is now 2TB per extent for a total size of 64TB in VI3.  Just something to keep in mind if you run into problems with 2TB+.  

However, you don't want to make them too small either for several reasons.  If the LUNs are too small, it will be hard to ensure enough growth per VM into the future, and you could end up painting yourself into a corner.

The number that I hear most often from the VMware people is 500GB LUNs, but with VI3, I definitely think that the average will start moving towards 1TB-2TB per LUN.  Like I said, just make sure you spread your I/O across as many spindles as possible.
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What about just sizing LUN's n general?  Without vmware is it better to have one big LUN or smaller ones?
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In general if anything is twice as big as another it will take four times as long to defragment or run a consistency check. Twice the number of blocks to compare with twice the number of blocks = polynomial time to solve.