Mac Pro: a solution for 2nd hard drive noise

Adding a second internal SATA 2 hard drive can make your normally whisper-quiet Mac Pro quite a bit noisier. Here’s a solution that worked for me.

I added a second hard drive to my Mac Pro to allow easy daily backups. I didn’t want an external firewire/USB drive as they seem to have strange spinup/down behaviour (at least my LaCie does) and you need to remember to power it on. Yes, I know you can put it on the same power strip, but…

Whilst the automatic daily backups are now working great, the extra noise created by the addition of the second drive is unpleasant to someone who likes a quiet machine.

It appears that Apple used metal drive carriers that attach to guides in the chassis. This allows vibrations from the hard drives to transfer to the case. Whether this was a wise decision, I don’t know, but it doesn’t seem to be the quietest solution, even though it certainly is incredibly quick and easy to add an extra drive using their system. Perhaps using some rubber insulation on the drive carriers could have reduced the vibrations and noise?

With one drive running at 7200 RPM the noise is hardly noticeable. However, it appears that when you have two or more drives installed, this causes significant vibrations and, therefore, noise to be generated.

Bearing in mind that I normally only need the second drive to be spinning and mounted to perform the daily backup, the 2nd drive needs to be operational for some short period each day. My initial idea was to: (1) avoid automount of the drives at system boot time and (2) to have a cron job which mounts the drive to perform the backup and then unmounts and detaches the drive after the backup has been performed. To cut a long story short, it seems that this may be possible, but due to the fact that Apple (or FreeBSD?) has nobbled the standard UNIX/Linux way of using /etc/fstab to specify how volumes are attached, I didn’t have any luck with this idea. Plan B was needed.

In the end, I reached a reasonable solution which was to modify the backup process to launch when the machine is booted, and then to run a short bash script I wrote to tell the second drive to be quiet. Here it is — the ‘hdoff’ script:

#!/bin/bash

# Unmounts the specified volume and then detaches the disk it's on.
# This causes the disk to spindown and so the Mac is a lot quieter.

# This is the volume which you wish to unmount
volume=/Volumes/Backup

# Use hdiutil to unmount the volume, grab the first field in the string hdiutil returns,
# then strip the "" characters, leaving just the bare disk name. Then detach the disk. 
disk=`hdiutil unmount $volume | awk '{print $1}' | sed 's/"//g'`
hdiutil detach $disk

echo "The volume '$volume' has been unmounted and its disk detached ($disk)."
echo "Enjoy the silence."

If you need to access the drive any time, just remount it, either using a script like above (hdiutil mount volume?) or open Disk Utility, select the volume and click on the Mount button. Nice! Grrrrreat.

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