Why does secondary disk spin up?

interesting question, I'd like to know this as well. all I can tell you is that the same thing happens with external disks on my imac. when I start applications like google chrome they awake from sleep without any reason to do so, which is really annoying (and bad for the drive)

Several things are a bit off here... first of all, an SSD is a "solid-state drive", meaning that it is flash memory and thus has no moving parts. So an SSD cannot "spin up." Second, the Superdrive is the optical drive, and I cannot imagine that replacing that with a different kind of drive is an Apple-supported modification. It would be difficult to say what problems might be caused by doing this.

I imagine that what you hear spinning is not a hard drive - if you can hear the hard drive spinning in your MBP, there's something wrong with it (I've never been able to hear the hard drive in any of my Mac laptops over an almost 10 year period), and as mentioned an SSD doesn't spin anyway. The fan in a MBP, however, can become quite loud if the machine gets hot enough. I'd imagine an SSD would generate some additional heat inside your MBP, thus increasing the chances of your fan becoming audible.

Thomas,

I'm sure j.koopmann realizes that by replacing his SuperDrive with an SSD (➚) he invalidated his warranties with Apple. He also mentioned that he now uses the SSD for his primary drive; hence, he expects the original HDD to never spin up. I agree with your guess that it might actually be the fan that's spinning up, not the HDD.

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J.Koopman,

You should install a hardware monitor (➚) to see whether or not it really is the fan that's spinning up when you hear the whirring sound.

Well, he said:

I use the original hard drive for data/media only. I noticed however that Finder and other apps tend to _spin up that disk as well_

(Emphasis added by me.)

I took that last bit to imply that he thought he had two drives spinning. However, that may have simply been the way I read it.

nachdenki,

If you've set those applications to save files (downloads, temp, swap, backups, etc) to your external drive, then they will likely do a volume check on first run. If they have a function that remembers the last locations accessed (recently opened/used/etc), they might do a volume check. If your drives have a software monitor that reduces wait times for accessing the drives, then it will usually wake the drives from sleep whenever it detects an activity that might require the drives (allowing you to quickly get to your files when you start up applications).

carlo, thanks for the response, but honestly: that's weird behaviour in my eyes. Waking up a large drive can take up to 10 seconds (mine is a little faster, but it still takes 5 seconds or something). during that time, the application is completly unresponsive. and why does starting chrome has anything to do with my external drive? sure, if I save something to the drive it obviously has to be woken up. but even if I just bring up a save dialog in an application, the external drive starts to spin, although I'm not even planning to save there nor am I looking at any files on the external drives.
this is extremly annoying, since you cannot disable drive-sleep for external drives and applications often have to wait for the external drive to spin up which slows down my work and makes the whole mac OS feel sluggish. it has in fact become so annoying that I unmounted all external drives and only mount them when needed - something I didn't want to do since I wanted everything to work automatically.

this wouldn't be a problem if the drive would be ready in a second or something. but it seems unlogical to me to make the user wait several seconds because he MIGHT wants to save to the external except make him wait when you KNOW he wants to do that.

j.koopmann wrote:
I am pretty sure it is not the fan.

Have you turned on the energy saver option to "Put the hard disk(s) to sleep when possible"? There seems to be positive outcomes in that regard at the end of a corresponding MacRumors thread (➚). I'm not able to test this myself, so I can't vouch for the last three responders in that thread.

Maybe perhaps there is a hardware check happening in the background, which might be spinning up your internal drive to confirm it's still there and not dead (but that's just a random guess). As long as electricity is reaching your HDD it's possible that basic firmware processes (like those that occur during bootup) might occasionally wake your drive. I'm just guessing at this point, so I don't think I'm gonna be much more help here.

nachdenki wrote:
this is extremly annoying, since you cannot disable drive-sleep for external drives and applications often have to wait for the external drive to spin up which slows down my work and makes the whole mac OS feel sluggish.

I don't disagree with you. I was just listing probable culprits for what's happening. I myself have four external drives attached to my Mac, and they too wake whenever I select Open/Save in any application. Fortunately, this does not inflict the slow down on my system that you are describing on yours (my dialog pops up immediately, even while the external HDDs are only beginning to spin up).

and why does starting chrome has anything to do with my external drive?

Perhaps Google wants to index your drive to optimize the relevance of your search results? I've not noticed whether or not my external HDDs also wake when I launch applications. I suppose since I do not experience the slow downs that you do, I've never paid attention; I'll keep an eye on it for next time.

A.Carlo wrote:
I've not noticed whether or not my external HDDs also wake when I launch applications.

Confirmed; opening up System Preferences woke up my external HDDs (probably related to the Startup Disk and Time Machine options). Apparently this is just the way OS X behaves (regardless of which app is launched). Still have no idea why nachdenki's machine gets the beach ball of death, whereas my machine doesn't (my Mac doesn't wait for my external drives to fully wake and spin up before moving on to the next process).

How do you unmount the disk? Do you right-click on the disk the Finder and select "eject?"

I find "eject" spins the disc down right away ("unmount" does not) and is more likely, but not always, to keep the disc spun down.

From the terminal, you can use: diskutil eject <drive name>

When ejected, I find that disks only spin up when an app crashes or I run Disk Utility.

@j.koopmann
This is kind of an old thread, but I am curious how it's turned out for you. I have the same setup, except that my Macbook's main drive is SSD and I placed my data disc in the optical bay.

So far I've found that my secondary drive (the HDD) is always constantly spinning, even if I'm not using it. When I eject it, I immediately hear a very obvious "spin down" and my computer becomes almost dead silent. However, when I put my laptop to sleep and wake it up again, the HDD, which is still unmounted, will spin up again, and stay spinning for about 5-10 minutes before sleeping.

I would really like for the HDD to sleep except when I'm getting data from it. Any ideas?

I'm in the same situation as the OP (Koopmann). I have a 15" MBP. I pulled the HDD and put in an SSD, then I removed the Optical Drive and put in a 750GB HDD.

I only keep Aperture data on the HDD (even my iTunes data is on the primary SSD). Anyway, after reading this thread it dawned on me that Spotlight might be the culprit. I went and added my HDD to the privacy settings of Spotlight (ie do NOT index), but it's still spinning up.

Again, not a big deal, more of a curiosity for me than anything. I'm just wondering why the OS (or some firmware) is spinning the drive up every few minutes.