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Kan-O-Z
Dec 5, 2008, 10:55 AM
I remember reading somewhere that SSD does not have a problem with fragmentation. Is that because of the way it stores data on the drive or is it because it has incredible random access as opposed to sequential access.

If SSD does not suffer from fragmentation problems does that mean OS X will not try to defrag it. What I'm really trying to get at is this:

As a general rule of thumb, it's ideal to keep at least 10% of your drive free so that the OS can use this space for defrag purposes increasing speed/efficiency. If SSD doesn't suffer from this stuff, does that mean we can go ahead a fill up most of the drive and still be efficient?

Kan-O-Z



silverblack
Dec 5, 2008, 11:37 AM
If SSD does not suffer from fragmentation problems does that mean OS X will not try to defrag it.

I don't know the answer, but I don't think (purely speculation) you can turn off the 'defrag' the OS X does regularly in the background.


If SSD doesn't suffer from this stuff, does that mean we can go ahead a fill up most of the drive and still be efficient?



Yes. This article (http://www.barefeats.com/mbpp08.html) shows that SSD does not slow down significantly as it fills up.

h1d
Dec 5, 2008, 07:56 PM
OS X does defrag in the back?

And from what I read (sorry forgot where) the way SSD works does not slow down by random reads (as many benchmark says), thus defragmenting the files doesn't mean much, and what's bad is if you actually do defrag it, the SSD life span just decreases. Seems, SSD has a block size that can be larger than a small file and if one were to erase a file that is smaller than a SSD block, the entire block has to be deleted and if any other part of another file was within the same block, it has to be moved before the deletion too, thus making alot of write operation when you defrag.

So, while the life span of SSD (especially MLC type) isn't big of an issue these days, I wouldn't do it when it doesn't make things better.

Catfish_Man
Dec 5, 2008, 10:16 PM
OS X does defrag in the back?

It does; when it attempts to open a file of less than 20MB that is in (iirc) more than 6 fragments, it will move it to a contiguous block if possible.

Nermal
Dec 5, 2008, 10:24 PM
It's true that SSDs don't suffer from fragmentation. In fact, Windows 7 won't automatically defrag the drive if it's an SSD. As h1d has mentioned, defragging an SSD will reduce its life, so it'd be a good idea to see whether the OS X auto-defrag can be turned off.

h1d
Dec 6, 2008, 02:27 AM
It does; when it attempts to open a file of less than 20MB that is in (iirc) more than 6 fragments, it will move it to a contiguous block if possible.

Ah, I didn't know. Wonder what happens if an app tries to open alot of small files at once, would it simply slow down badly?

And is some kind of daemon doing the work or is it built into the file system (or kernel) and can't be turned off unless choosing another file system?