Q: `hdiutil` Option "-notremovable" Doesn't Work

Thoughts, but no obvious solutions.  it's unlikely that the hdiutil utility changed that much from 10.5 to 10.6 to 10.7. That suggests that there's something peculiar about your 10.6 installation that's producing different behavior.  Best thing to try as a diagnostic is to boot into safe mode on 10.6 and see if you still have the problem.  If not, then something you did to your system is getting in the way.

I'd also suggest (as a general rule) that you avoid this kind of complex syntax.  Mount the disk in one line, then erase it in the next.  Trying to do it all in one line looks cool, but I wouldn't trust it to be consequence-free.

well, I switched into my 10.6 partition and tested.  I see the problem you're having, and it seems to be a function of diskutil, not hdiutil.  when I split the commands up, the hdiutil segment works correctly, but diskutil throws the following errors:

Started erase on disk2

Unmounting disk

Erasing

newfs_hfs: write (sector 0): Cannot allocate memory

Mounting disk

Could not mount disk2 with name (null) after erase

Error: -9944: File system formatter failed

apparently in 10.6 there's some kind of bug in creating the file system in this context. 

I'm not sure why you're using diskutil here anyway.  wouldn't it be easier just to create the file system using hdiutil?

Hi,

I sucessfully created a notremovable ramdisk by adding the option -kernel when using the tool hdid. Tested on Mac OS X 10.6.8.

Cheers,

snow-punk

Attention, the following lines are not ready for a final script, cause they contain the sudo command. I post here just the ready-for-terminal version of my tests.

#creating the disk

name=ramdisk

#size in MB

size=64

device=`sudo hdid -nomount -kernel -notremovable ram://$((2048*$size))`

sudo diskutil erasevolume HFS+ $name $device

#testing stuff

touch /Volumes/$name/test

ls -l /Volumes/$name

hdiutil detach $device

ls- l /Volumes

ls -l $device

sudo hdiutil mount $device

ls -l /Volumes/$name

The testing stuff section shows that I have no clue atm, how to remove the device later. So it will be existing and maybe consuming RAM until next reboot. So I guess when scripting this, one has to persist the $device name on which the ramdisk was created. Checking the existence of $device via

test -e $device

and then deciding, to run the create command with diskutil if the $device has not been created or just mounting the already existing $device.

If you or somebody else finds a way to remove the notremovable , I d appreciate to read a solution here.

//snow-punk

Try this:

     sudo /usr/bin/hdid  -notremovable -nomount -kernel ram://128000

Show the ouput here if it is not a device name.

Then if the 1st command was successful do:

     sudo /usr/sbin/diskutil erasevolume HFS+ "webfolder" <DEVICE_NAME>

<DEVICE_NAME> is the output of the command before.

Show the output here, if you still need a third eye.

Btw your two liner has spaces arround the operator = . This is not correct bash syntax.

//snow-punk

Ok I think there are some things you can evaluate:

1. Do a self-developed backup (maybe as a periodical launchdaemon script) which utilizes the power of rsync. Some inspiration can be found here: http://hints.macworld.com/article.php?story=2011010204203424

That way you can keep a hdd folder in sync with your ramdisk and simply let timemachine backup that hdd folder.

2. I read something about an unsupported option in timemachine to add some include paths to the timemachine:

http://superuser.com/questions/285225/how-to-make-timemachine-back-up-contents-o f-any-path-or-mounted-volume

If that works, one problem might be to assure that the ramdisk is always mounted when the backup happens (the discussion about that is included in the link above). Maybe switch off the standard Timemachine scheduler and use a more advanced one: http://www.klieme.com/TimeMachineScheduler.html

It supports auto-mounting unmounted drives. Ok it just auto-mounts the Backup-drive, but I think there is a chance to modify the daemon that is installed by TimeMachineScheduler and wrap around some script code that also mounts additional devices. But all this is very theoretical, as far as I understand your case, your ramdrive is always mounted. I just wrote that down for other use-cases than yours.

3. On the size limit of 1024MB. Well maybe creating multiple ramdisks and a set of symlinks can help out here. Depends on your application, and what you are doing with the ram space.

One comment to the notremovable: For me this option solves one major problem I had with ramdisks:

Without that option my ramdisk very often vanishes if I closed my macbook's lid or if I just switch from airport network to LAN network.

looking into

     ls -l /dev/disk?

showed me that also the device has been removed in that situation.

But now with the notremovable flag, the volume still gets unmounted when the magic system event network-change happens. But, surprise surprise, the device under /dev/ still exists and so a simple

     hdiutil mount /dev/disk<some_number>

brings my ramdisk and all its contents back.

I think I can script this to happen automatically and I am happy now.

So in my opinion the ramdisk is now much more not removable than before.

Good luck,

snow-punk

PS: If cosmetics matter: the drive icon can be changed via CMD+i dialog on the volume. The change is stored in some hidden files on the volume then.