SQL Server IO Subsystem

I am currently revising the IO setup in relation to our main SQL Server 2005 instance.

At the moment we have all data, logs and backups all on one LUN.

I have been allocated 4 LUNS which I was thinking of using as follows:

  • LUN1 = Data Files
  • LUN2 = Transaction Logs
  • LUN3 = Backups

Now for LUN4 for I was thinking of either putting system databases here Master, Model, Temp or putting heavily used databases on here, which would be the most logical approach?

I guess I am just looking for suggestions as to how others would split this up.

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asked Nov 09, 2009 at 07:02 AM in Default

helixia gravatar image

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I agree with Kev, TempDB is often under heavy load and should be separated from the rest of the files. One thing to remember with Luns and SAN, is that even if you have different Luns you cannot be sure that the different Luns are using their own set of harddrives, unless you divide your SAN into disk groups.

Make sure you have as many fast disks as possible in your diskgroup, do not focus on the space requirements for your datebase. Some companies buy few but large disks to their SAN to save money, but they loose performance.

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answered Nov 09, 2009 at 08:01 AM

Håkan Winther gravatar image

Håkan Winther
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+1 - this is valuable information - there is no guarantee that a LUN represents anything in particular. For example, your LUN1 could be spread over 30 disks, and LUN2 LUN3 and LUN4 might all share two disks. Without knowing the physical implementation behind the LUNs it's not possible to make a judgement about whether moving data between them would be beneficial.
Nov 09, 2009 at 08:09 AM Matt Whitfield ♦♦

That is a really good point. To be honest I would like all LUNS to have there own disk groups except maybe the backups LUN as this will only be used overnight.

I will include that in my report, from reading up it seems like LUNS 1,3 & 4 would be best suited to use RAID5 or RAID 1+0 and LUN 2 to use RAID 1 for heavy writing.
Nov 09, 2009 at 08:23 AM helixia
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The best thing to do is to TEST in your environment. Do a server-side trace on a typical production workload and then replay this in a test environment with and without the tempdb LUN and benchmark your results. Base your decision on real-world testing. Sometimes you will get unexpected surprising results.

Based on my own testing, I have placed tempdb on the same LUN as the data files because placing it on a separate LUN for my workload did not achieve anything except complicating the setup slightly.

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answered Nov 09, 2009 at 12:57 PM

Mark Allison gravatar image

Mark Allison
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Are your LUNS using separate diskgroups in the san? Make sure they are, because if your LUNS are using the same set of disks you cannot expect any improvements.
Nov 10, 2009 at 04:44 AM Håkan Winther
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Using LUN4 for TempDB is a good idea.

It's always useful to separate Tempdb from user db where possible.

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answered Nov 09, 2009 at 07:31 AM

Kev Riley gravatar image

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asked: Nov 09, 2009 at 07:02 AM

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Last Updated: Nov 09, 2009 at 07:33 AM