Detect SSD in Mac OS X (Cocoa)

Question

Is there a reliable, quick, deterministic way (definitely not benchmark) to check whether system drive in Mac OS X is on Solid State Drive?

Is there any other indicator how well disk handles parallel access? I'm trying to adjust number of threads that my program is going to use for disk-bound operations.

I'm not interested in raw speed or seek time, only which type of access – serial or parallel – is faster for the drive. I don't expect users of my program to use iSCSI or RAID. SSD is my focus, anything else is nice-to-have.

Device Characteristics of IOAHCIBlockStorageDevice contains this information. How can I read it programmatically?

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So far I've figured out it goes like this: (following is pseudocode)

match = IOBSDNameMatching(kIOMasterPortDefault,0,"disk0s2");
IOServiceGetMatchingServices(kIOMasterPortDefault, match, &iterator);
while(entry = IOIteratorNext(iterator)) {
   do {
     entry = IORegistryEntryGetParentEntry(nextMedia, kIOServicePlane, &entry);
     dict = IORegistryEntryCreateCFProperty(nextMedia, 
            CFSTR(kIOPropertyDeviceCharacteristicsKey), kCFAllocatorDefault, 0);
     [dict objectForKey:CFSTR(kIOPropertyMediumTypeKey)];
   } 
   while(!dict && entry); 
}

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Edit: Here's complete source code. I've verified it works with Intel SSD and OCZ Vertex.

Answer 1

Actually, I think you should go the benchmarking route, because it more accurately answers your question - you don't really care that the disk happens to be an SSD, you just care that the disk is really fast. What if the user is using a fast RAID setup, or a Fiber Channel array, or is using iSCSI?

Just read a bunch of random sectors from the underlying /dev/diskX and if it meets your requirements you can treat it as a "Fast" drive

Answer 2

The number of threads? 1 is going to overwhelm any disk, SSD, RAID or not. Disk is slow, processor is fast. The OS is going to reorder your disk requests anyhow (or at least it should) to get the least head movements.

Answer 3

If you're trying to get that kind of information, you're best guess is IOKit.

You can try some of it's functionality using the ioreg command line tool or the IORegistryExplorer.

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Here's some code that might help you. It fetches all hard drives that aren't a RAID and aren't partitions. This isn't what you want, but it might get you started.

http://pastie.org/782219

I'll see tomorrow if I've got more time to provide a solution if this didn't help you enough.