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Yes, Virginia: Windows *DOES* Defrag SSDs (Sometimes)

Two persistent myths that attach to SSDs running under “modern” Windows OSes (version 7 and higher) are as follows:
(a) defragging such disks is a bad idea
(b) Windows doesn’t defrag such disks by default, provided that it recognizes them properly.

Visiting the Windows 8 Forums this morning I saw a tantalizing post from regular (but anonymous) contributor “A Guy,” entitled Does Windows defragment your SSD? This, in turn, led to a nice article by Scott Hanselman that addresses the subject in some detail. This screen shot, from my own Windows 8.1 Update 3 system reveals that the Optimize Drives utility in Windows 8.1 does indeed perform *periodic* defrags of SSDs when (as is the case on my system) restore points are enabled for those drives:

Hanselman cites “the Windows storage team” to affirm that volsnap copy requires optimization to keep the number of file fragments on an SSD below the allowable maximum.

Volsnap is shorthand for the Volume Shadow Copy operation used to capture a snapshot of the drive to be used as a restore point, which then becomes available to the System Restore operation to roll the drive back in time to when the snapshot was taken. During this operation the file system follows metadata used to link file fragments together to “stitch them up” into a single logical extent that comprises all the individual physical file extents of which they’re made. If the number of fragments exceeds a critical maximum value, the file system can’t keep up with the fragments any more (and file copy or access operations can fail). This can’t be allowed to happen so Windows schedules optimization on SSDs by default on the same day every month, starting from the day that the OS is installed (or if System Restore has been turned off for a drive, on the day that it gets turned back on).

That’s why as you can see in the preceding screencap that Optimize Drives does indeed report a “Last run” date for SSDs that have System Restore turned on. And despite the advice of many “Optimize SSD” guides available on the Web to turn off System Restore for such drives, Hanselman cites some good evidence from an unimpeachable source — the guys responsible for making Windows filesystems behave properly on all available storage devices, including SSDs — that this is probably not a good idea from both a performance and reliability standpoint. Hanselman’s summary is worth quoting in this context: “…Windows is not foolishly or blindly running a defrag on your SSD every night, and no, Windows defrag isn’t shortening the life of your SSD unnecessarily.” Furthermore “Yes, your SSD’s file system sometimes needs a kind of defragmentation and that’s handled by Windows, monthly by default, when appropriate.”

Very interesting and informative!