Mac Running Hot, Slow, & Fans Blazing After Installing OS X Lion? Here’s Why
We’ve received a fair share of comments and emails about Mac OS X Lion making some Macs seem sluggish, running hotter than usual, and causing the machines fans to run at full speed. This sounded concerning, but after I went about installing Lion DP4 myself and looked into this a bit further I’m here to report there’s nothing wrong, and here’s what’s going on.
Why is the Mac running hot? The explanation is simple: Spotlight. Yup, Spotlight and it’s worker modules mdworker and mds are at it again. When you update to Lion 11A480b, whether you are upgrading from 10.6 Snow Leopard or just from Lion DP3, your Spotlight index has to rebuild itself, and depending on the Lion installation volume, this can take a while.
After Spotlight is done indexing though, your Mac may still be blazing away and running slower than it should. This is also normal, and that’s because right after Spotlight is done indexing the drive, Mac OS X Lion will rebuild it’s system caches by running kextcache, and this is also CPU intensive activity:
You could get away with killing the Spotlight processes, but you definitely don’t want to do this with kextcache, and the Mac OS X Manual for kextcache tells us why – “Caution: Incorrect use of kextcache can render a volume incapable of startup.” Let kextcache run or you could screw up your fresh Lion installation.
It’s hard to give a time estimate for how long these two normal system functions should take, but on my MacBook Air there was a good 20 minutes of blazing fans and sluggish performance while the CPU was consistently pegged over 100%. The time for Spotlight to index may take even longer if you did a dual boot partition scheme because Lion will most likely try and index your Snow Leopard installation as well. You can always click on the Spotlight menu to get an ETA, but it’s not always accurate and it won’t include the kextcache process.
See, no big deal. Finally, you have to remember this is a developer preview and not a final release OS. It’s clear that the excitement for Lion has caused usage and installation by a wider community than developers alone – heck a handful of my non-dev friends alone shelled out the $99 to get developer access just so they could run Lion – but I think this is adding to some of the confusion about system performance. This is absolutely not a Lion system compatibility issue, it’s normal system behavior. Just let this stuff run and your Mac will be happy.