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We have a Dell R710 that had serious hardware issues last Friday evening. Dell replaced the mobo and processor, and the machine booted fine. The server runs Win2k8 R2 Server Core, and hosts 4 VMs, all Win2k8 R2. One of the VMs runs SQL Server 2008 R2. Storage is RAID10 SAS 15k.

I have a few benchmark queries for SQL server that take about 30 seconds to run. After the repairs from Friday, they now take about 60 seconds to run. I can't figure out what's causing the drop in performance. The configuration for everything has not changed, only the mobo and processor. Any ideas on what I should be looking at?

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@Tonny - Thanks! The issue was Active Power Management was enabled in the BIOS, which forced the processor to run at half speed (~1600 Mhz), as shown by CPU-z. Even as my SQL VM spiked to 100% CPU usage, the processor speed on the host remained at half speed. I changed the power setting to Maximum Performance and now it continually runs at full speed. See for more info on this. – John Galt Nov 10 '11 at 14:22
up vote 4 down vote accepted

Are you sure the bios is configured correctly ? Most default bios configs on motherboards ship with Hyper-threading and VT-x disabled. That just might make all the difference, especially with VM's. Also possible that the bios on the new board is an old version and doesn't recognize a new CPU properly causing it to run at lower frequencies.

Of course they could really have saddled you with a slower CPU than you used to have.

Don't believe what Windows is telling you about the CPU and the speed. This could be totally bogus. (Either because Windows doesn't know about this particular model CPU or because it hasn't realized there was a CPU change and it is happily reporting the values from the previous CPU.)

Use CPU-z: This will always pull the info from the CPU itself and tell you what is really there in much greater detail than Windows.

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+1 for a check of the bios and settings. What was the old processor? What is the new processor? How many? – Mike Walsh Oct 25 '11 at 14:53
You could also call Dell tech support. – jftuga Oct 25 '11 at 14:59
That said it is uunlikely an older processor takes database benchmarks (NORMALLY IO limitd) down by 50%. – TomTom Oct 25 '11 at 15:05
Slower CPU doesn't always mean older CPU. In some cases there are newer models that are slower (but less power-hungry) then previous models. Or a newer CPU (newer than the bios that is) is not recognized by the bios and treated as an older/slower model getting a wrong (to slow) clock/multiplier combination. – Tonny Oct 25 '11 at 15:25
if its running hyper-v then it wouldn't even boot the vm's if vt-x was disabled. – tony roth Oct 25 '11 at 16:11

I would say look at the standard set of performance counters you look at whenever you are baselining SQL Server (Brent Ozar has a good post about SQL Server performance counters).

Look at system utilization. Hopefully you have before pictures as well to compare against. If not, look for resources that appear to be bottlenecks.

I would also look at the server logs to ensure all things are running at their best, both on the host and the guest. Look at the hardware logs and the manufacturer's open manage/power manage/etc. tools.

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Thank you -- this was helpful. The SQL VM showed 100% CPU usage during queries, but they were still taking twice as long. This led me to look at the CPU on the host, which was running at half speed. – John Galt Nov 10 '11 at 14:18

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