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Placement of SQL Server Data and TLog files in a SAN Infrastructure and Monolith Storage Environment Expand / Collapse
Posted Tuesday, April 15, 2014 9:59 AM

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Andy sql (4/15/2014)
There is no way that a single SQLIO exe, running on a single server, should be able to bring down your SAN!

If you know that you are not allowed to run a stress-test tool, then an alternative is to simply copy a large MDF file between partitions, and measure how long it takes. Not exactly scientific, but is a real-world situation.

To Stress test a SAN's storage you have to run against the LUNs presented and to ensure you saturate the SANs cache, and doing that - as I have done a few years back when I had such a chance to test the SAN infrastructure before going into production - will stress the SAN and will dramatically slow it down, causing problems for applications. If you don't do this, then the figures are useless in telling you at what load the IO subsystem can handle.

I also know it is possible to bring a SAN to its knees because on another gig I did, where I was brought in to help with a SQL Server performance issue for a well known high-volume internet sales site, the incumbent DBA had brought their systems down when he carried out a 'stress-test' using SQLIO without telling anyone he was doing the work.

Sorry, but no apology for my comments here.
Thanks anyway

Edit: I've added links here that are helpful to the points I raise...

Post #1561957
Posted Wednesday, October 1, 2014 12:16 PM



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(1) how important, performance-wise, is it to separate out these files?
->it is easier for management in case you decide to reorganize storage. Logfiles have mostly sequential reads, datafiles are mostly random io. Logfiles could be moved later to fast sequential disks (smaller capacity but more) and some datafiles to flash-storage (great reads)
(2) is there a benefit in having the data and tlog files on separate windows volumes (ie, storage-based LUNs), based on the fact that all the data is spread across the whole of the storage array anyway?
->Same as above, allows for easier storage tiering/isolation/monitoring/redirection when seperate
(3) will having separate volumes (ie, storage-based LUNs) mean that there will be separate paths for the data to travel to and from the storage array through the SAN fabric, will this help with performance, and if yes, how?
->It probably generates seperate paths, depends on the storage/fabric if there is some quality of service. There can be paths with high priority (like fast fabric) and with lower priority (slower fabric in case fast gets overloaded).
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