# PCs: Any Dangers to Defragging...? **URL:** \ **Category:** Factual Questions\ **Created:** [August 17, 2003, 2:42am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699 "2003-08-17T02:42:18Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 17, 2003, 2:42am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/1 "2003-08-17T02:42:18Z")
I wish to defragment my hard drive overnight. Are there any pitfalls, dangers, or side-effects for which I should FIRST be aware? Is there the potential to lose files, barring a power outage? Any other things come to mind? If it matters, I am running Windows 2000 Professional. Thanks, - Jinx ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 17, 2003, 2:46am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/2 "2003-08-17T02:46:14Z")
I’ve had a PC crash in the middle of a lengthy defrag. Things ran hellishly slow after rebooting and the disk was massively fragmented, since the defrag was in the midst of shuffling files around, but it got back up and I ran the defrag again with no problems. I can’t say for certain that zero files were lost or damaged, but I never noticed if there were. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 17, 2003, 2:54am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/3 "2003-08-17T02:54:39Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*I’ve had a PC crash in the middle of a lengthy defrag. Things ran hellishly slow after rebooting and the disk was massively fragmented, since the defrag was in the midst of shuffling files around, but it got back up and I ran the defrag again with no problems. I can’t say for certain that zero files were lost or damaged, but I never noticed if there were. \*\* Barring such catastrophic events, it should be ok, correct? - Jinx ---
**Author:** ![emmaliminal](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@emmaliminal](https://boards.straightdope.com/u/emmaliminal)\ **Post date:** [August 17, 2003, 3:00am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/4 "2003-08-17T03:00:18Z")
Most defrag programs warn you to run a disk-checking program first; if there are any problems in your files or on your machine, you want to fix those before you go moving them around. Just In Case. ---
**Author:** ![SkyBum](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@SkyBum](https://boards.straightdope.com/u/SkyBum)\ **Post date:** [August 17, 2003, 3:05am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/5 "2003-08-17T03:05:28Z")
It’s actually quite an important step in keeping your machine running efficiently. I have never heard of a single downside to defragging. Any _possible_ downside would have to be miniscule in comparison to the benefits. A computer networking consultant friend of mine _swears_ that one should _always_ defrag before installing new software. For the most part, I have made a habit of following his advice. Just my two cents… ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 18, 2003, 3:24am UTC](https://boards.straightdope.com/t/pcs-any-dangers-to-defragging/195699/6 "2003-08-18T03:24:57Z")
There is a small but real danger in running defrag. The defrag is doing a lot of updating to the FAT tables. If the system crashes before one of those updates completes, that file could end up corrupted. So don’t trip over the power cord, do it at a time when power failures are unlikely, etc. A well written defragger can practically avoid this problem. So that of course means that the one that ships with MS OSes shouldn’t be used. Note that this can occur with any program that writes disk files but since a defragger is doing this constantly, it’s more of a concern. A defrag can also turn up a hidden problem. E.g., a sector of the disk is going bad, it was occupied by an unused file but an important file is moved there. But this is a disk problem that needs fixing. It’s not really defrag’s fault. Defragging can speed up some computers by amazing amounts. Go ahead and do it regularly.