After replacing 128GB SSD with a 500GB one in my 7 year-old MacBook Air, I’ve noticed a serious issue… Since 4GB RAM is very limited (and not designed) for the contemporary macOS, it runs out of memory very often especially when I opens multiple tabs in browser and edits photo in Lightroom simultaneously. It isn’t a big deal because there is swap mechanism, which stores data to disk when the (physical) memory is not enough. However, since the SSDs have finite numbers of P/E (program / erase) cycles, the more intensive the swap uses, the sooner the SSD would be worn out. The lifetime of SSD basically depends on its type of NAND flash. For the SSD I installed, WD SN750 500GB, it uses TLC NAND and declares it has 300TB-write endurance.
Unfortunately, if the SSD is used as system disk with limited RAM, it will be worn out rapidly by the swap mechanism. For example, my MacBook with new SSD has powered on for 161 hours, and it has been written for ~663GB data(!). To tackle this issue, I should either upgrade my MacBook ($) or try to limit the usage of memory by disabling swap and doing minor tweaks.
1. Disable swap
Be careful! Disable swap would cause kernel panic if there is not enough RAM for processes. Take it at your own risk.
1.0. Disable SIP
From macOS 10.11 to present, there is a built-in system integrity protection (SIP) for preventing malicious modification. To disable swap, first we have to turn SIP off.
- Power-off MacBook first, hold Command (⌘) and R, and then start-up the MacBook.
- You should see a macOS utilities window.
- From the utilities menu, select “Terminal”
csrutil disableand press return, the screen should display a message the SIP is already disabled.
- From the menu, press restart to restart MacBook.
1.1. Disable swap
To check the current mode that system manages memory, type
sysctl -a vm.compressor_mode in terminal. The default mode is
4, which represents compressing memory and using swap. To disable swap, we should change the mode from
2, which means compressing memory only.
sudo nvram boot-args="vm_compressor=2". Again, anyone running computer without swap file should monitor memory usage carefully to avoid kernel panic!
1.2. Enable SIP (Recommended)
After disabling swap, we should enable system integrity protection (SIP) again for security reason. The steps are similar to disabling swap, and the only difference is the command. Type
csrutil enable instead to enable SIP. If you want to disable
spindump furtherer (listed below), you should enable SIP later.
2. Disable unused processes
Here we use
unload two services, and rename the files.
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.spindump.plist
sudo mv /System/Library/LaunchDaemons/com.apple.spindump.plist /System/Library/LaunchDaemons/com.apple.spindump.plist.bak
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.tailspind.plist
sudo mv /System/Library/LaunchDaemons/com.apple.tailspind.plist /System/Library/LaunchDaemons/com.apple.tailspind.plist.bak
mds stands for “metadata server”, which is a part of Spotlight in macOS. It indexes for all devices to provide effective search functionality. If you never use Spotlight, you could disable it for saving CPU and memory usage.
To prevent it from indexing all devices, type
sudo mdutil -a -i off in terminal.
If you want to enable it again, just replace the command with
sudo mdutil -a -i on.
2.2. Disable Adobe CC services
Although Adobe provide amazing products like Lightroom and Photoshop, its background services consume memory and CPU even when the Adobe-related program is not running.
The service corresponding to Adobe CC services is located at
/Library/LaunchAgents/com.adobe.AdobeCreativeCloud.plist, to prevent it from auto-launching from log-in, we will use
launchctl again: type
launchctl unload -w /Library/LaunchAgents/com.adobe.AdobeCreativeCloud.plist in terminal.
To enable it, just replace
load in the command.
3. Tab suspender
If you open a lot of tabs in the browser every time like me, you should consider suspending inactive tabs while you are not browsing the website or AFK, to limit the memory usage of browser. The following method is recommended. It is risky to use third-party extensions such as The Great Suspender since it might contain malware.
Microsoft’s Edge has announced built-in “sleeping tab” feature recently (2020/09). To enable it, simply go to Settings → System → Save resources.
Furthermore, you can modify timeout to suspend the inactive and set the allow-list in the configuration page.
A. SMART monitor tools
brew install smartmontools
After installing, you can run the command in Terminal.app:
smartctl -a disk0
disk0 is the device name referring to the inspected disk. Device name can be found via Disk Utility.app:
Device information such as serial number, temperature, bytes written and read will be shown in the terminal. Note that some NVMe admin commands are not supported currently via
smartctl, therefore some detailed NVMe information will not be shown correctly.