在MACOSX中設置RAMDISK

換了SSD後，為了空間，（因為經費有限，只能買128G的SSD）
考量了SSD使用年限，於是找了一下設置RAMDISK的方式。

設置方式如下：
1. 啟用「noatime」：新增檔案「/Library/LaunchDaemons/com.nullvision.noatime.plist」，檔案內容如下。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
        "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>com.nullvision.noatime</string>
        <key>ProgramArguments</key>
        <array>
            <string>mount</string>
            <string>-vuwo</string>
            <string>noatime</string>
            <string>/</string>
        </array>
        <key>RunAtLoad</key>
        <true/>
    </dict>
</plist>

2. 變更檔案權限。

sudo chown root:wheel /Library/LaunchDaemons/com.nullvision.noatime.plist

3. 重開機。

重開機後，執行
$ mount | grep " / "
/dev/disk0s2 on / (hfs, local, journaled, noatime)
應該會有noatime的字串出現

4. 新增「RamFS」的目錄，與修改目錄權限。

cd /System/Library/StartupItems
mkdir RamFS
sudo chown -R root:wheel RamFS
sudo chmod -R u+rwX,g+rX,o+rX RamFS

5. 新增檔案「/System/Library/StartupItems/RamFS/RamFS」，檔案內容如下。

#!/bin/sh
# Create a RAM disk with same perms as mountpoint

RAMDisk() {
    mntpt=$1
    rdsize=$(($2*1024*1024/512))
    echo "Creating RamFS for $mntpt"
    # Create the RAM disk.
    dev=`hdik -drivekey system-image=yes -nomount ram://$rdsize`
    # Successfull creation…
    if [ $? -eq 0 ] ; then
        # Create HFS on the RAM volume.
        newfs_hfs $dev
        # Store permissions from old mount point.
        eval `/usr/bin/stat -s $mntpt`
        # Mount the RAM disk to the target mount point.
        mount -t hfs -o union -o nobrowse $dev $mntpt
        # Restore permissions like they were on old volume.
        chown $st_uid:$st_gid $mntpt
        chmod $st_mode $mntpt
    fi
}

# Test for arguments.
if [ -z $1 ]; then
    echo "Usage: $0 [start|stop|restart] "
    exit 1
fi

# Source the common setup functions for startup scripts
test -r /etc/rc.common || exit 1
. /etc/rc.common

StartService () {
    ConsoleMessage "Starting RamFS disks..."
    #這邊可以設定RAMDISK的SIZE。512表示是512MB的意思。
    RAMDisk /private/tmp 512
    RAMDisk /var/run 64
    #RAMDisk /var/db 256
    #mkdir -m 1777 /var/db/mds
}
StopService () {
    ConsoleMessage "Stopping RamFS disks, nothing will be done here..."
    # diskutil unmount /private/tmp /private/var/run
    # diskutil unmount /private/var/run
}

RestartService () {
    ConsoleMessage "Restarting RamFS disks, nothing will be done here..."
}

RunService "$1"

6. 新增檔案「/System/Library/StartupItems/RamFS/StartupParameters.plist」，檔案內容如下。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/PropertyList.dtd">
<plist version="0.9">
    <dict>
        <key>Description</key>
        <string>RamFS Disks Manager</string>
        <key>OrderPreference</key>
        <string>Early</string>
        <key>Provides</key>
        <array>
                <string>RamFS</string>
        </array>
        <key>Uses</key>
        <array>
                <string>Disks</string>
        </array>
    </dict>
</plist>

7. 把「~/Library/Caches」移到RAMDISK中。（可做可不做，重開機的話，Browser的cache,cookie,history都會消失）

cd ~/Library
mv Caches Caches.old
ln -s /private/tmp Caches

8. 把hibernate的功能關掉：hibernate檔案的SIZE是依照記憶體大小來配置。所以如果RAM是4G，hibernate的檔案就是4G。而MACOSX只有在電池快沒電時，才會使用到hibernate的功能。用到的機會幾乎等於0，建議把hibernate的功能拿掉，可以節省不少空間。方式如下：

$ sudo pmset -a hibernatemode 0
$ sudo rm /var/vm/sleepimage

9. 重開機

==
Reference:
Mac OS X SSD tweaks
Mac OS X SSD tweaks (revised for 10.6.5 – thanks to Pierre)