Don’t wake up external hard disk when saving to internal one

external-diskhard drivesleep-wake

My problem is that I have an external hard drive connected to my Mac. Since it is only used for backup purposes, it is sleeping most of the time.

However if I now want to save something (e.g. a picture from a website) to my internal hard disk, I have to wait for the external one to wake up before the "save as…" dialogue appears.

I know about the question How to save a file quickly and no need to wait for the external hard drives to "wake up"?, but it sounds like it intends a solution about not letting the hard disks go to sleep whereas I would like to let the external hard drive have its well-deserved rest.

EDIT:

I do not want to unplug it, because I know that I will forget to reconnect it before the automatic backup
various other operating systems deal very well with situations like that

EDIT2:

Using Sherwood Botsford's answer I put together the following AppleScript which mounts the hard drive, executes for example an rsync and unmounts it again.

do shell script "diskutil mount 'Name of your Volumn'"

do shell script "rsync -av --delete ~/ '/Volumes/Name of your Volume/.'"

do shell script "diskutil unmountDisk 'Name of your Volume'"

Best Answer

possibilities.

A: Unmount the disk from the command line.

diskutil unmountDisk Lacie

would be the command to unmount a disk that has a file system named Lacie on it. You can also refer to the device itself, but devices can vary from one mount to another. unmountDisk will take any file system name as the object but will unmount all other file systems if the drive has more than one.

Then, when you want to do a backup,

 diskutil mount Lacie

You also need to disable spotlight from indexing this drive.

Related Solutions

IMac – How to save a file quickly and no need to wait for the external hard drives to “wake up”

The save button is checking all mounted drives, and will spin them up.

Your only way I can think of to do this is to prepare a couple of scripts.

See the man page for diskutil. If the mount point (diskname) is BigFatDisk

then to unmount the disk it would be something like

diskutil unmount BigFatDisk

Now to keep everything sync'd to BFD you would run a script now and then

diskutil mount BigFatDisk rsync flags local disk BFD diskutil unmount BigFatDisk

A second option is to replace the disks in the BFD enclosure with hybrid disks. These have an SSD chunk and a spinning rust chunk, and are ideally suited for this.

A third option is to let your disks spin whenever the machine is awake? The amount of power they use is small, and increasingly MTBF times are being given as X spinups, not X hours. A hard drive 2 years ago used 5-7 watts. I'm sure it's better now. So let's use 5. That works out to 40 kWhr per year, roughly. At 15 c per kWh that's 6 bucks/year. Seems to me that this is pretty cheap compared to the hassles you have now.

I have set my computer to turn the screens off after 20 minutes idle time, but never to turn off the CPU or spin the drives down.

Mounting an external hard disk clone that shares the same partition GUIDs as the source/host hard disk

I have tested your set-up in a virtual machine with the same result - the second CoreStorage volume won't be mounted. Cloning a CoreStorage container to another disk with dd doesn't change the UUIDs of the CoreStorage items. So it's indeed a problem of the duplicate UUIDs of the Logical Volume Group/Physical Volume/Logical Volume Family/Logical Volume of disk0s2 and disk3s2.

The good news is: there is a man entry for a tool which can change the UUIDs of all CoreStorage metadata objects: man csunique.

Check the disk identifier of the duplicate with diskutil list. In your example that's disk3s2.

Then the command in your case would be:

csunique -v -n /dev/rdisk3s2 #dry-run
csunique -v /dev/rdisk3s2

The bad news is: I can't find the tool/script. It's neither in the path nor can I find a file with this name elsewhere on the disk. I checked this in 10.9/10.10/10.11/Recovery HD by searching the whole disk even inside packages with FileBuddy. A Google search wasn't successful.

Work in progress

You may change the various UUIDs manually by editing the raw disk content with a tool like HexEdit or wxHexEditor of course. AFAIR the pvUUID and the lvgUUID are located at the first block of disk3s2. The pvUUID/lvgUUID has several additional occurrences in the metadata area of the Logical Volume Group of disk3s2. Don't use arbitrary (ie self-made) UUIDs but try to generate them with uuidgen or online with a UUID generator. Some bits of the UUID have a special meaning and determine UUID version or the hash algorithm.

Example:

The diskutil cs list output of the original disk:

diskutil cs list
CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group C451C0F6-32F9-43AB-8E59-42D21AEFF650
    =========================================================
    Name:         SystemCS
    Status:       Online
    Size:         67859718144 B (67.9 GB)
    Free Space:   18948096 B (18.9 MB)
    |
    +-< Physical Volume E46EF8F2-6399-45C1-B213-8628A518466D
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     67859718144 B (67.9 GB)
    |
    +-> Logical Volume Family AAD268A6-FC66-43FC-A24E-11A1F23CA5DD
        ----------------------------------------------------------
        Encryption Status:       Unlocked
        Encryption Type:         None
        Conversion Status:       NoConversion
        Conversion Direction:    -none-
        Has Encrypted Extents:   No
        Fully Secure:            No
        Passphrase Required:     No
        |
        +-> Logical Volume 50B61719-7CB4-40D9-8AFC-F5CD37C1A66C
            ---------------------------------------------------
            Disk:                  disk3
            Status:                Online
            Size (Total):          67488448512 B (67.5 GB)
            Conversion Progress:   -none-
            Revertible:            Yes (no decryption required)
            LV Name:               SystemCS
            Volume Name:           SystemCS
            Content Hint:          Apple_HFS

The pvUUID (light violet) and lvgUUID (light yellow) appear in hex in the first block and the last block of the partition:

1st block:

last block:

and as text each four times in the last 32760 blocks (512 byte physical block size) of the partition in plist-like items.

Best Answer

Related Solutions

IMac – How to save a file quickly and no need to wait for the external hard drives to “wake up”

Mounting an external hard disk clone that shares the same partition GUIDs as the source/host hard disk

Related Question