Improve Your Disk Performance
Regardless of your drive’s raw speed, if lots of processes are trying to read/write at the same time, that’s going to dent your Mac’s overall performance—even with a fast CPU and lots of RAM. (The problem is much less severe, but not entirely absent, with SSDs.) In this chapter, I talk about what some of those disk-intensive activities are and how to minimize their impact. In addition, since your Mac can run slow if its startup disk becomes critically low on space, I explore numerous ways to address that problem. And I discuss a few other ways (of varying degrees of utility) to increase a disk’s performance.
Tame Disk Access
Earlier, in Disk Speed, I said that your hard disk can do only one thing at a time. If you ask it to do two or more things at once—reading, writing, or searching files—it can accomplish this only by switching back and forth between the tasks rapidly, which slows all the tasks down. Even an SSD, which doesn’t suffer from the physical constraints of mechanical hard disks, can read or write data from only one location at a time, so giving it too many things to do will reduce its performance.
Apart from ordinary file access, macOS often uses your disk to store virtual memory swap files. If the software you’re running makes demands for memory beyond the physical RAM you have installed, macOS moves pages of memory onto and off of your disk as needed. As I detailed in RAM, although a little of this may go unnoticed, the more heavily macOS is forced to depend on virtual memory, the greater the amount of disk thrashing. That will slow down your Mac all by itself, but when you combine it with other disk-reading and -writing activities, it’s bad news all around—your Mac could freeze up. (And the best remedy, of course, is to Add RAM.)
How might you know if your disk is being overworked? If your Mac has a mechanical hard drive, you might hear it clicking and whirring away, depending on where the Mac is located, the type of disk, and the ambient noise level. But you can get a better idea if you Use Activity Monitor: click Disk at the top of the window, and you’ll see a graph with reading activity shown in blue and writing shown in red. In normal use, both of these spike from time to time, and if you’re reading a large file (such as playing a movie in iTunes) or writing a large file (for example, saving an iMovie project), one or the other might stay high for a while. But if you’re seeing sustained high reading and writing activity for no apparent reason, sort the processes on Activity Monitor’s Disk tab by Bytes Written (to see what’s writing data) or Bytes Read (to see what’s reading data). When you identify the culprit, you can decide whether to let it continue with its task, quit it, or change its settings.
A few types of disk activity warrant additional discussion: Spotlight, backups, and other disk-intensive software.
Control Spotlight Indexing
Spotlight is the system-wide mechanism in macOS for indexing and rapidly searching files. Some people love Spotlight, and some hate it. I won’t ponder its many merits and faults in this book, nor do I intend this to be a general Spotlight troubleshooting guide. For our current purposes, I want to focus on one aspect of Spotlight: the way it hammers on your disk when it’s indexing your files—what that might mean for your Mac’s performance, and what to do about it.
The first time Spotlight encounters a new local disk, it automatically reads and indexes the contents of every single file on that disk—a process that can take many hours, depending on the number of files and the speed of the disk. (By default, Spotlight doesn’t index network volumes, except for Time Machine volumes. You can change that by entering commands in Terminal or by using various third-party utilities, but that’s beyond the scope of this book.)
After its initial time-consuming indexing run, Spotlight updates its index whenever you add or modify a file, and, in theory, that indexing should happen so rapidly that you never notice it. However, you might notice it if you add or change lots of files at once—or if a bug in Spotlight, or damage to one of its files, confuses Spotlight and causes it to reindex loads of data.
If your Mac seems unaccountably slow, you’ll probably Use Activity Monitor to see what’s up. When you do, you can tell that Spotlight is busy indexing because Activity Monitor will show high CPU usage for mdworker and/or mds. It’s normal for these processes to spike briefly from time to time, but if they remain high for a long time, with no apparent reason (that is, you didn’t recently mount a new volume or modify a lot of files), you’ll need to take steps to settle Spotlight down. Alas, merely quitting the mdworker and mds processes won’t do the trick, because they’ll restart on their own.
So, you have several choices, each with its own pros and cons:
Erase your Spotlight indexes and start over. If Spotlight’s incessant indexing is due to errors in its index files, you can delete them and let it index everything all over again. The downside: this will take hours, during which time your disk will be quite busy. And you have no way to know for sure, in advance, whether a bad index was to blame, so all that time might be for nothing. On the other hand, if it does work, you’ll benefit by having less disk activity and a fully functional Spotlight index. To do this:
Open Terminal (in
/Applications/Utilities).Enter this command, followed by Return:
sudo mdutil -E -aEnter your administrator’s password when prompted.
Spotlight then reindexes all your volumes; be prepared to wait many hours before searching works again. I recommend starting late in the day so Spotlight can run overnight.
Add volumes to Spotlight’s Privacy list. Any folder or volume that you add to Spotlight’s Privacy list won’t be indexed. So, if you added all your disks to this list, nothing would be indexed! However, newly attached disks that don’t appear in the list would still be indexed. And note that not only does this disable content-based searches, it even prevents you from searching by file name. If that’s what you prefer, do this:
Go to System Preferences > Spotlight.
Click Privacy.
Click the plus
button, navigate to a volume you want to exclude from Spotlight, and click Choose. Repeat as necessary for any additional volumes.
Spotlight removes its indexes for the selected volume(s) and discontinues indexing them.
Disable Spotlight altogether. If you absolutely hate Spotlight and never ever want to run the slightest chance that
mdworkerormdswill use 0.1% of your CPU, you can disable it, but I’m not going to tell you how, because I recommend against it.Disabling Spotlight entirely also prevents searches in Mail from working, keeps you from finding files with Time Machine, and has other undesirable side effects—and the improvement in your Mac’s overall speed versus simply turning off indexing for individual (or all) drives is minuscule. Go ahead and Google it if you must, but really…please don’t disable Spotlight.
Wrangle Uncooperative Backup Software
Backups are an essential part of modern computing life, and I’ve long advocated the use of multiple, complementary backup systems (for example, a bootable duplicate stored on an external hard drive, versioned backups using Time Machine, and online backups from a provider such as Backblaze). Unfortunately, some backup software can also slow down your Mac considerably when it runs. I’d never advocate giving up backups to get a speed boost (or, frankly, for any reason) but you can minimize the impact of backups on system performance.
The main reason backups may slow down your Mac is that they read lots of data from your disk—sometimes going so far as to scan every single file (and there may be millions of them) multiple times every day. All that disk access means other processes that read and write files have to compete with your backup software for the disk’s attention. Depending on the backup software you use and how it’s configured, it may also use lots of CPU power when compressing or encrypting files, network bandwidth when sending your data to another computer, and other valuable resources.
Before you take action, make sure backups are indeed causing your system to slow down. If you notice that your Mac isn’t as responsive as usual, you can glance at the Time Machine icon in your menu bar to see if it’s running, or check Activity Monitor to see if backupd (for Time Machine) or another backup app is near the top of the list for CPU usage. Even if it is, you might leave well enough alone if it’s only an occasional spike, because the benefits of regular backups are so great.
Once you’ve determined that a backup app is slowing down your Mac and that you’re unwilling to live with that slowness, you can fundamentally do three things:
Change the backup software’s settings so that it’s less intrusive.
Switch to different backup software.
Stop backing up your Mac.
Obviously, I don’t recommend the last option, so let’s look at some ways you can alter settings or use less resource-intensive software.
Adjust Backup Software Settings
Here are a few ideas for settings you might be able to change that could significantly reduce your backup software’s performance penalties:
Exclude problematic files. Virtually every backup app offers a way to exclude items you want to avoid backing up. (For example, if you use Time Machine, you can go to System Preferences > Time Machine, click Options, and then drag items into the exclusion list.) If you have large files that change frequently, you might choose to exclude them from regular (say, hourly) backups and instead back them up manually, or at least less frequently, when they’ll cause less of an interruption. Files that might fall into this category include large videos and VMware Fusion virtual machines. (Parallels Desktop stores its files in a more backup-friendly format.)
Make sure you’re doing incremental backups. Most backup software automatically does incremental updates—that is, each time it runs, it copies only the files (or portions of files) that are new or changed since its previous run. However, this isn’t always the default choice, and a few less-capable backup apps don’t offer it at all, instead insisting on copying every file, every time they run. Yuck!
Schedule backups for when you’re away. Backups that run frequently throughout the day increase the chances that you’ll be able to recover lost work, but they can also bog down your Mac just when you’re busiest. If you find that to be the case, see if you can schedule your backups to happen just once a day—perhaps in the middle of the night or during lunch breaks, when you’re not using your Mac anyway. (You will, of course, have to leave your Mac on if you do this!)
Time Machine doesn’t give you this option, alas. You can turn off Time Machine and back up manually by choosing Back Up Now from the Time Machine menu in the menu bar (or its Dock menu). Or you might try a third-party tool, such as TimeMachineEditor, that lets you alter Time Machine’s default once-per-hour schedule.
Schedule more frequent backups. This is more or less the opposite of the last point, and it sounds counterintuitive, but hear me out. If your backup software does not scan or index all your files every time it runs, then most of its time is spent simply reading and writing files that have changed since its last run. The less frequently you back up, the more data it’s likely to have to copy, and the longer it will take. So, if you schedule the software to run more frequently, it should take less time during each run because there’s less data to copy. Of course, this trick doesn’t work with backup software that begins each run with a complete disk scan, but in many cases it’s worth a try.
Be careful with multiple backups. Perhaps you use multiple backup apps for different purposes—say, Carbon Copy Cloner, Time Machine, and Backblaze. That’s no problem in theory, but if you have two or more backup apps scanning your disk and reading files at the same time, that’s bound to cause a more significant performance hit than any single backup app. If you think this might be your problem, try turning off all but one of your backup apps—just as an experiment—for a day or two. If that fixes the slowdowns, consider either altering the apps’ schedules so they don’t overlap or choosing one or more different tools that give you the flexibility to prevent this sort of collision.
Try a (benign) hack. Earlier, in Adjust Priority on the Command Line), I discussed using the
renicecommand in Terminal to change a process’s priority. That won’t let you speed up Time Machine backups, but there’s another way, detailed in Massively speed up Time Machine backups by Keir Thomas at Mac Kung Fu. With that procedure, you use Terminal to enter an obscure command that prevents Time Machine from reducing its priority in the background, thus making it run much faster. (The article details a separate procedure to make this change survive a restart.)I tried this tip myself and found that it did indeed make Time Machine much zippier. Some of the article’s comments suggest there could be undesirable side effects (like other processes besides Time Machine running at high priority), but the change is easy enough to undo if you discover problems after running it.
Consider Changing Your Backup Software
Mac users have dozens of choices when it comes to backup software; I provide a set of detailed feature comparison tables in the online appendixes for Take Control of Backing Up Your Mac. If you’re unhappy with your current backup software, look for a replacement with one or more of these attributes:
Delta encoding: Backup software that can copy only the portions of files that have changed since last time, rather than the entire files, may be faster, especially if it’s copying to network destinations. On the other hand, it takes extra CPU effort to compare the new version of the file with the old in order to identify the changed portions, so in practice this feature could be a wash performance-wise (depending on many variables).
Scanning aids: Some backup apps use the macOS FSEvents (file system events) framework to find out almost instantly which files have changed since their last run. This dramatically reduces the time necessary to scan all your files manually each time your backups run and, in some cases, enables continuous, real-time backups as your files change (see the next point). Other backup software scans and copies in a single pass, arguably a more efficient approach than scanning all your files and then making another full pass to copy them.
Continuous backups: Some backup apps eschew conventional schedules, at least optionally. Instead, they actively watch for files to change (per the previous bullet point) and then immediately—or after a delay you specify—back them up. This largely avoids the heavy, sustained disk access that occurs when backup software copies a great many files at once during a scheduled run.
Manage Other Disk-Intensive Software
Although backup software is particularly notorious for heavy disk access, several other categories of software also tend to do a great deal of searching, reading, and/or writing. If you use this software and it slows down your Mac, all I can recommend (aside from, you know, not using it!) is to try to isolate disk-intensive apps so that only one of them is running at a time—and avoid doing other work that relies heavily on your disk when these apps are in use.
Examples of disk-intensive software include:
Anti-malware software: As I explained in Eliminating Malware, such software is as unlikely to find malware as it is likely to slow down your Mac.
Syncing tools: If you use software to keep folders on two or more Macs in sync, it could produce a great deal of disk access, depending on the quantity of files you sync.
Image editing: Photoshop and other image editing apps can access your disk heavily, especially when you’re working with high-resolution photographs and applying complex filters.
Media recording and encoding: Pretty much any app that records or encodes audio or video is likely to use your disk heavily. Merely playing a song in iTunes barely touches your disk, but recording (or even playing) videos, ripping CDs and DVDs, and recording or editing multitrack audio (using GarageBand, for example) will give your disk a workout.
Searching and indexing utilities: Spotlight, as I mentioned earlier in this chapter, accesses your disk extensively. But if you choose not to use Spotlight and go with a third-party tool of some kind to search for files on your disk, your disk will still be heavily in use during the indexing (and, in some cases, searching too).
Disk repair utilities: Perhaps it goes without saying, but if you run Disk Utility or third-party software to examine and fix problems on your disk, that will involve a great deal of disk activity.
Free Up Disk Space
At the risk of beating the horse I killed when discussing the myth of Freeing Up Disk Space, increasing the amount of available space on your startup disk does little or nothing to improve your Mac’s speed unless it’s extremely close to being full. (Of course, as discussed in RAM, if you’re short on RAM and the macOS virtual memory system starts writing large swap files to your disk, it can fill up in a hurry even if it looks like you have several gigabytes of free space.) And if you’re close to capacity, the best long-term solution, if you can afford it—and assuming your Mac allows it—is to upgrade to a larger disk (see Upgrade Your Hard Drive or SSD).
If, however, your disk is close to being full and you can’t upgrade it, don’t panic. In this section I offer numerous suggestions for giving yourself extra breathing room.
Determine How Much Space You Need
All right, how much available disk space should you have? I’ll tell you, but you may not like the answer: it depends.
Over the years, I’ve frequently read recommendations to leave at least a certain percentage of your disk space available—but the amount various people suggest has ranged from 5% to (no kidding) 50%! The truth is that it’s not a simple matter of some magical percentage.
Let’s suppose, for the sake of discussion, that you have an older Mac with a 250 GB hard disk, of which 50 GB (20%) is empty, and you’re having no problems; in day-to-day use, the macOS virtual memory swap files and other temporary files never come close to filling that up. Now imagine that tomorrow you upgrade your drive to a 2 TB model. If you continued to feel obligated to leave 20% of your drive empty, that would now be a whopping 400 GB—much larger than your old drive! That makes no sense, because macOS will still never touch most of that space. If 50 GB of available space was enough with the smaller drive, it’s enough with the larger drive too, even though it’s only (in this example) 2.5%.
Let’s look at how much empty disk space you really need, based on the types of files that must be written during normal operation of macOS:
Virtual memory swap files: All things being equal, the more RAM you have, the less space you need for these files, although the number and size of swap files can increase over time as apps make increasing demands on the system. For most people, 1 GB of empty space for swap files should be plenty as long as you restart fairly regularly. In any case, the maximum total size of swap files on disk seldom exceeds 4 GB under typical use—and the more RAM you have, the less likely you are to get near that figure. (To learn more about virtual memory swap files, refer back to RAM.)
Sleep images: As I discuss later in Manage or Disable Safe Sleep, notebook Macs by default use a feature called Safe Sleep, which involves writing the entire contents of RAM to disk when the Mac goes to sleep. If you have such a Mac and have this feature enabled (or enable it in the future), you’ll need to have free space on your disk equivalent to the amount of RAM installed.
Scratch space: Certain classes of apps—particularly graphics apps such as Photoshop and video apps such as iMovie—need a fair amount of temporary storage called scratch space to enable them to perform complex operations on large files, maintain undo/redo capability, and so on. If you never use such apps, you need not worry about scratch space; if you use them heavily, it would be fair to say no amount of scratch space is too much! As a bare minimum, though, I suggest you have 1 GB that could be used as scratch space; adjust this number (most likely upward) depending on your needs.
Caches: Some apps cache files more aggressively than others. Web browsers, for example, tend to accumulate especially large caches, as do certain types of backup software (including Backblaze). I suggest leaving at least another 1 GB free to hold these files (in addition to any caches already on your disk).
Files, logs, and temporary data from open apps: You should be sure to have enough space to save files from apps you have running, which may include your email client, Dropbox, and other software that can accumulate data in the background. In addition, many apps store records of errors, warnings, and other notifications in constantly expanding log files, and quite a few create temporary files of various sorts that don’t cleanly fit into any of the categories already mentioned. Just to be safe, I recommend setting aside 500 MB to enable any open apps to save these types of data.
Automatic defragmentation: macOS needs its own scratch space of sorts for automatic defragmentation (see Defragmenting and Optimizing Your Disk); to be generous, I’ll suggest leaving another 500 MB free.
Grand total? Let’s call it 4 GB plus, if it’s a notebook, the amount of physical RAM in your Mac. (Of course, if your notebook Mac already has a sleepimage file, as I discuss in Manage or Disable Safe Sleep, that extra space is already effectively set aside.) Elsewhere in this book (see Add RAM) I urge you to install plenty of RAM, and I hope that most readers will end up with at least 8–16 GB of RAM, depending on their budget and their Mac’s capacity (although some may be limited to as little as 2 GB). So I think it would be fair, as a first pass, to estimate that the minimum amount of space you should leave empty is 6 GB or twice the amount of RAM installed, whichever is larger. And you’ll notice that figure has nothing to do with the size of your disk!
This rule of thumb doesn’t scale indefinitely. Once you get to about 100 GB of available space, I’d say you’re in good shape regardless of how much RAM you have. If you have, say, 128 GB of RAM in an iMac Pro with 1 TB of storage, it’s a bit unrealistic to keep 256 GB of storage space free!
Keep in mind that if you have only that minimum amount of space available when you turn on your Mac, a lot of it will disappear as you go about your business (though much of that will be reclaimed the next time you restart, as certain files, such as virtual memory swap files, are purged automatically; see Restart Your Mac). So think of this number as the lowest amount of disk space you should ever see on your Mac, even when it’s been running full-tilt for weeks. (How can you keep an eye on your disk space in real time? See Use Live Monitoring Tools.)
I want to reiterate that this minimum number is approximate. Because you’re always going to be generating new data as you use your Mac, it’s unwise to skate too close to this minimum. It’s enough to get you through your current session, but if you’re that tight on disk space you need to take action to give yourself room to expand in the future.
When you discover that you need more disk space, you can do any (or all) of the following things to get it.
Use Optimized Storage in Sierra or Later
If your Mac is running Sierra or later, one handy way to free up disk space and reduce the rate at which clutter accumulates is to use Optimized Storage features in macOS. With these features, macOS automatically purges outdated caches, logs, and other unneeded system files, and asks if you want to delete downloaded disk images after installing software from them. In addition, you can enable several optional features:
Choose Apple > About This Mac > Storage and click Manage.
In the list on the left, select Recommendations (if it’s not already selected). The options available to you will vary based on which settings you’ve already selected, but by default you can opt for any or all of the following:
Store in iCloud: To move your Desktop and Documents folders to iCloud Drive or enable optimized storage of your iCloud Photo Library (or both), click Store in iCloud, select one or both of the checkboxes, and follow the prompts.
If you select Desktop and Documents, those two folders will be moved to iCloud Drive (and thus copied to Apple’s servers); if you enable this feature on other Macs, those folders will sync with the other Macs too. macOS automatically removes older files from your Mac if you start running low on disk space—but the files’ icons remain in place, and if you attempt to open the files later, macOS downloads their content automatically. (Note that if you choose this option, you may need to purchase additional iCloud storage from Apple.) Before you enable Desktop and Documents, think about how much space the items in those folders occupy and the impact of syncing them on your iCloud storage space and your internet provider’s data cap, if any. You may find, as I do, that space and financial considerations lead you to forgo this option.
Optimize Storage: Click Optimize and follow the prompts to instruct macOS to remove from your disk any movies or TV shows from the iTunes Store that you’ve already watched (you can download them again later if you like, as long as they’re still available from Apple). You can also have Mail download only recent attachments, or no attachments at all—again, those can be downloaded on demand if needed.
Empty Trash Automatically: Click Turn On (and confirm by clicking Turn On again) to have macOS automatically remove items from your Trash that have been there for 30 days.
Reduce Clutter: Click Review Files to show large files, downloads, and other items you might want to delete.
Once you’ve enabled any of these features, macOS will perform the necessary tasks in the background from then on. You’ll be less likely to run out of disk space, but Optimized Storage does not by any means eliminate the need for other types of manual maintenance.
If you still need more free space after enabling Sierra’s Optimized Storage features, read on for further suggestions.
Find and Delete Large Files
When you need to free up disk space fast, it pays to start by looking for the low-hanging fruit—namely, the largest files on your disk. Numerous utilities can scan your disk(s) and display all their files—even the hidden ones—by size. (Spotlight can do this too, but requires a bit of fiddling—and you may have disabled Spotlight indexing for some of your data.) Some of these utilities give you a simple list, while others offer a nifty graphical display that makes it easy to see how various files compare in size. Once you’ve identified the largest files, you can delete those you don’t need, or move ones you do need to a different drive.
Examples of tools that can help you find large files easily are:
Delete Duplicate Files
Another category of files you can easily delete are exact copies of files that are stored elsewhere on your disk. These can be difficult to find by hand, but a few utilities can make short work of the process, pointing out duplicate files so you can decide which, if any, should be deleted:
Uninstall Unneeded Apps
If you’ve installed software that you no longer use, you can free up disk space by deleting it. This is especially true for large, complex apps such as iMovie, GarageBand, and the components of Adobe Creative Suite. Unfortunately, uninstalling is rarely as simple as dragging a single file to the Trash; most apps have numerous components scattered on your disk (and the space occupied by these components tends to be larger when the app itself is large).
Even if you installed an app by dragging an icon into the /Applications folder, the app may have added files to numerous other folders (such as ~/Library/Application Support and ~/Library/Preferences) as you used it. Some apps helpfully include a custom uninstaller, an uninstallation function within the installer, or at least explicit instructions from the developer as to how to find and remove all those extra pieces. In other cases, completely uninstalling software can be a challenge.
Fortunately, numerous utilities exist that can do all the hard work. All-purpose uninstallers can automatically delete files associated with particular apps wherever they happen to be on your disk, so you don’t need to find them manually.
Here are a few examples:
CleanMyMac—my favorite; see my TidBITS review (of an earlier version), Save Space and Uninstall Apps with CleanMyMac 3
Remove Unneeded App Resources
Many macOS apps contain components that take up disk space but that you’ll never use. For example, if an app has been localized into a dozen languages other than English, it might contain 12 copies of all the help files and all the text and images associated with language-specific interface elements. And, if it’s a Universal Binary, it contains code for both PowerPC and Intel processors—but modern Macs don’t have PowerPC processors, so they don’t need both sets of code.
It’s possible to strip out these extra resources if you don’t need them, and in some cases this can dramatically reduce file sizes—which not only frees up space on your disk but also reduces the amount of space and time required to back up your apps.
In principle, you should be able to remove unused resources without any ill effects whatsoever, as long as you’re careful not to remove your native language or the native code for the type of processor you’re using. However, in practice, some apps break badly if you try to remove any of their guts, even parts that are seemingly useless. (Adobe Creative Suite apps are often cited as examples.) In addition, removing resources might appear to work initially but then cause problems later when you attempt to update your software.
For these reasons, I’m hesitant to recommend this procedure except in cases of extreme disk shortage that can’t be solved any other way (such as on a small SSD)—and even then, I urge you to proceed with caution. By “caution,” of course, I mean make a full backup first, proceed slowly, and test every app thoroughly after pruning its resources. You should hang onto those backups, too, at least until after the app’s next update, in case any problems arise.
Examples of utilities that can remove unneeded language and architecture-specific resources are CleanMyMac and Monolingual.
Move Files to Another Disk
If you get to the point of having removed all the files you can live without but you still need more space on your startup disk, you must offload some of your files to another disk—perhaps a second internal disk, if your Mac can accommodate one; an external Thunderbolt, USB, or FireWire drive; or even a network volume.
To move a file or folder from one volume to another, you can do either of the following:
Copy the item to the other location, drag the original to the Trash, and then choose Finder > Empty Trash.
Hold down ⌘ while dragging the item to its new location. This moves it (copies it and deletes the original) in one step.
In general, you can freely move any file or folder within your home folder to another disk and continue to use it normally. (I recommend leaving your ~/Library folder alone, though, because it contains files various apps depend on.) However, some apps look in specific places for their data, and if you move that data the apps can get confused about where to find their files, unless you tell them explicitly. So I’d like to give you slightly more detailed instructions for two common apps that fall into this category and tend to store a great deal of data, too: Photos and iTunes.
Move Your Photos Library
To move your Photos library to another volume:
If Photos is running, quit it.
In the Finder, navigate to
~/Pictures.Hold down ⌘ and drag the Photos Library icon to its new home. (The ⌘ key causes the Finder to move the library rather than copy it.)
Once the data finishes moving to the new location, press and hold the Option key while opening Photos. A prompt appears, asking which library you want to use.
If the newly moved library already appears in the list, select it and click Choose (look at the folder path below the list to make sure you pick the right one). If not, click Other Library, navigate to the new location, select your Photos Library, and click Open.
Move Your iTunes Library
To move your iTunes library to another volume:
In iTunes, choose File > Library > Organize Library. Select the “Consolidate files” checkbox, click OK, and wait while iTunes copies to your iTunes folder any iTunes-tracked files that are currently located elsewhere.
Quit iTunes.
Move your entire iTunes Media folder from its current location—by default, in
~/Music/iTunes—to the new location. (Since you’re relocating it to another volume, hold down ⌘ as you drag and drop it, to move it rather than copy it.)Open iTunes again. Go to iTunes > Preferences > Advanced, and then click Change. Navigate to the new location of your iTunes Media folder, select it, and click Choose.
If a dialog appears that asks “Would you like iTunes to move and rename the files in your new iTunes Media folder to match the ‘Keep iTunes Media folder organized’ preference?” click Yes.
iTunes immediately begins using your relocated library.
Defragment and Optimize Your Disk
I warned you, back in Defragmenting and Optimizing Your Disk, that in most cases defragmentation and optimization are an utter waste of time. To fully defragment or optimize a disk, you’ll have to boot from another volume—not your usual startup disk—and let the process run for hours, or possibly even days. During that time you’ll be less productive (at best), and once the process is finished your disk might not be any faster than it was before. As far as I’m concerned, life is too short.
However, it wouldn’t hurt to defragment your disk now and then if:
You work extensively with large files that must be read or written in real time, such as video and audio, or…
Your disk has very little free space and you notice that it takes an unusually long time to open and save files.
There are two ways to defragment your disk, each with its pros and cons.
Use a Defragmenting Utility
One approach is to use a special utility that moves blocks of data around on your disk, reassembling them into contiguous wholes, consolidating free space, and updating the directory appropriately. This requires no additional hardware, but it is the more time-consuming method and does involve buying an app to do the job. Your choices include the following:
Follow the developer’s instructions to install and run the software.
Create and Restore a Bootable Duplicate
Another way to defragment your disk is to make a complete, bootable copy onto another disk, erase the original disk, and then start up from the copy and reverse the process. When your Mac writes data to an empty disk, it automatically makes the files contiguous.
You cannot make a bootable clone simply by dragging files onto another drive. You must use a specially designed utility, such as SuperDuper! or Carbon Copy Cloner.
This approach is considerably faster than using a defragmenting utility, and it costs less (potentially nothing) for the software. However, it does require you to have a spare disk to use for the duplicate.