Question to a developer ?

Since this is a user forum and there aren't any Apple employees, I'll respond, but from the standpoint of being a sometimes Linux kernel hacker...

First, spinning down drives isn't hedge against hardware failure, but an energy-saving feature. Truth is that spinning down drives doesn't impact hardware life. When drives are spun down, there's clearly no mechanical wear, but the act of spinning them up or down produces more wear than leaving them spinning. In the end, the increased wear of spin up/down is offset by the reduced wear of the idle state -- meaning the setting has no net benefit (or detriment) with regard to wear on the drive. Energy-wise, though, the impact can be substantial.

With regard to drive access... UNIX systems in general, and including OS X, use a considerable amount of caching on disk I/O. Writes can queue for a while and may flush when caches fill or when the system idles, and reads will be from cache unless the cache is polluted or an object isn't in a cache. Web browsers in particular do astonishing amounts of I/O - each graphical element is a file, cookies are stored in a database, Javascript can have local storage, Flash can write temporary files, documents are cached, images and links are preloaded, etc.

That said, most of those cache misses will affect the boot-disk. If other drives (like externals) are spinning up, then it may be any number of causes. First, there's periodic tasks that run in the background that defragment files, refresh indexes, etc. If you have security software, it will periodically enumerate disks for scanning (waking everything up), and there are models of external drives (mostly cheap USB models) that require that they be polled periodically or they go to sleep entirely and disconnect.

Disk accesses are generally asynchronous, however, and should not affect the browser. The only reason that it would block is if the browser is making a request for disk enumeration. That would only happen if the page has Flash or Java content that requests it. Normal HTML wouldn't have that issue. Unfortunately, both Flash and Java (not JavaScript) do have features whereby they internally request and accounting of all the attached volumes. When they make that request, they block the browser until the function returns. You could always ask Adobe or Oracle to address that.

Console seems to indicate that Safari is requesting a font for a webpage that didn't show up in FontBook or has some problem with it, and it's polling the harddrives to find it.

This drives me out of my mind...I have a big storage array and a few portables, so whenever it decides to do this I'm waiting a good 60secs for 10 drives to spin up one at a time.

If anyone here knows a convenient way to completely block access to a drive (leaving it plugged in, but mount/dismount quickly from the keyboard or something), or has an app that will keep them spun up at least for an hour or 2 at a time, let me know.

HDD's spinning down after 2min are almost certainly responsible for 20-23% of the world's homicides.

n/m SpindownHD.app in the Apple Developer CHUD package lets you set spindown times. I wish there was a way to block programs from accessing external data, like a Lil Snitch type program that prevents Safari from asking the OS for some irrelevant font in the first place.

(I'm running Safari 5.1 in OSX 10.7 at the moment, and it's not fixed there either...I'm not sure I even understand the need for more than 3 fonts in Safari anyway...the more stuff I disable—like fonts and Flash and Shockwave and Java—the better my life gets online.)