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We've all been told that defragmenting a hard disk is a good thing for performance, but the same is most definitely not true for flash drives.
Is it ever necessary to defragment a USB flash drive?
Defragmenting a hard drive makes sense to me because the hard drive read arm has to jump around the disk for fragmented files; but what about flash drives? If all the data is just stored in memory, it seems like accessing those memory addresses won't take any longer, whether they are consecutive or spread in different places. And if it is necessary to defragment a flash drive, then it seems like we could also argue that we need to defragment our RAM from time-to-time!
You've hit one nail squarely on the head: flash devices (or any "solid state" devices) don't gain a performance benefit from being defragmented.
But in reality things get worse. Much, much worse.
You should never defragment a flash drive.
Files are stored on hard disks in pieces; frequently in 512 byte chunks. Now, there's no requirement that these chunks be next to, or even near each other. That means that a file could have its contents spread out in totally random places on the hard disk. You normally never see this, because the file system takes care of locating all those chunks when you read or write a file.
On a traditional hard disk there's a physical read/write head that moves around on the media when data is being accessed. Much like the laser in a CD player (or the needle on a record player), the disk spins underneath it, while the head moves in and out to locate the proper "track" that contains the next chunk of the file that's being accessed.
Moving that read/write head takes time.
So, if you can ensure that all the chunks of a file are next to each other or "contiguous", the head doesn't need to move as much, and reading the file is faster.
And that's what defragmenting, or "defragging", a hard disk is all about: rearranging where on the disk the file chunks are stored so that when the time comes to access a particular file, all the chunks are together and the read/write head doesn't need to move as much.
Flash drives have no read/write head.
In fact, flash drives have no moving parts at all. Everything that makes it look and act like a hard drive is actually done by mimicking the characteristics of a hard drive in the flash drive's circuitry.
Defragging a flash drive will get you no performance benefits. Since there's no head to move, there's no additional time cost in fetching one chunk of data from a flash drive over any other. It doesn't matter how the files are laid out, it's all just as fast.
So now that I've convinced you that there's no point in defragging a flash drive, why did I say that you should never do it?
Writing to flash memory causes it to degrade ever so slightly. (Reading does not.) The more you write to a flash device the shorter its lifespan will be.
Now, don't get me wrong, "normal" usage should be just fine. And the technology continues to improve almost daily. Not only is the underlying technology improving, but the techniques to mitigate the problem are improving as well. For example, most flash drives try to "spread out" write activity across the entire device, so that even if you're constantly re-writing the same data over and over again, the device will "move it around" so you're not wearing a single spot on the device faster than any other.
But still ... flash memory wears out.
If you're regularly defragging a flash drive, you're adding thousands upon thousands of write operations each time you do so. Whatever the expected lifespan of the device, you could easily be cutting it in half or worse.
For no benefit.
(Full disclosure: OK, a reader did comment on a prior article with a potential benefit - defragmented files are easier for recovery utilities to recover. Fair enough. In my opinion that's not even close to a good enough reason to shorten your flash drive's lifespan. Use a good backup strategy instead.)
So defrag your hard drives every so often. But never defrag your flash drives, there's just no point.
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