Whats wrong with defragging an SSD?

[Guest]

I've never used an SSD before -but I plan to. In an off-topic thread about stupidest tech mistakes, a few people said the stupidest thing they'd ever done with computers is defrag an SSD. What's wrong with defragging? I don't know much about SSDs so would someone please explain?

[MegaDave91]

An SSD's life is determined by write cycles that you waste when you defrag.

[flibberdipper]

Reduces the lifespan of the NAND chips by doing a ton of write cycles.

[Altecice]

no benefit as SSD's don't really have seek time (the time it takes for the write head to find all parts of the file, so if its fragmented you can see why it slows down). Plus people are obsessed with the limited writes that you can do on an SSD (even though its in the billions) so in a sense it wastes writes.

[Guest]

Ah okay. So it's not a huge deal if I were to accidentaly defrag one?

[Enderman]

There is no need to defrag it because it is digital, not mechanical storage. All the data on an SSD takes the same time to access because there is no spinning disk like there in a HDD which has to move to where the data is.

Defragging is only for hard drives.

 

Defragging an SSD will wear out its nand flash cycles shortening its life span while giving 0 improvement.

[kirBi]

Ah okay. So it's not a huge deal if I were to accidentaly defrag one?

 

Accidentally doing it once or twice will be fine.

Doing it routinely over years can have negative impact on SSD.

BTW I don't think it's even possible to defrag SSD on recent OSs.

[aidenrelkoff]

Accidentally doing it once or twice will be fine.

Doing it routinely over years can have negative impact on SSD.

BTW I don't think it's even possible to defrag SSD on recent OSs.

my win8 tablet had it set to auto defrag every week.... i turned that off thankfully.

[kirBi]

my win8 tablet had it set to auto defrag every week.... i turned that off thankfully.

Huh, that's strange.

On my windows machines (windows 7 and windows 8.1) the OSs automatically recognized SSDs and removed them from the defrag schedule.

[Nakoron]

Huh, that's strange.

On my windows machines (windows 7 and windows 8.1) the OSs automatically recognized SSDs and removed them from the defrag schedule.

Not always. Install win 7 brand new comp 2 months ago and it was set to on. Install another ssd on another comp, it defaulted off. Both windows 7 - which is supposed to detect non moving drives and turn defrag off. Both Adata drives.

[hojnikb]

no benefit as SSD's don't really have seek time (the time it takes for the write head to find all parts of the file, so if its fragmented you can see why it slows down). Plus people are obsessed with the limited writes that you can do on an SSD (even though its in the billions) so in a sense it wastes writes.

Thats not true at all. Modern SSDs are only good for a few 1000 rewrites.

[Eric1024]

No one has mentioned the reason why it's actually useless to defrag an ssd: you can't. There's a layer of abstraction between the block addressees that the file system sees and the actual location of each block in the flash. The ssd controller keeps a mapping of this translation in order to be able to read the same logical blocks as the physical blocks move.

 

SSDs need this abstraction layer so that they can speed up read-modify-write operations. They redirect the write to a clean page somewhere instead of waiting for the old page to erase since erasing is slow. In essence, the flash controller moves the data to a physically different page on the drive, but from the perspective of the file system it hasn't moved.

 

Since the file system doesn't know where blocks actually are on the disk, it can't re-order them in any useful way. Thus, the fs can't defrag the disk.

 

This really isn't a problem though because ssds dont have seek latency, so it doesn't matter if blocks are contiguous or not.

[dalekphalm]

No one has mentioned the reason why it's actually useless to defrag an ssd: you can't. There's a layer of abstraction between the block addressees that the file system sees and the actual location of each block in the flash. The ssd controller keeps a mapping of this translation in order to be able to read the same logical blocks as the physical blocks move.

 

SSDs need this abstraction layer so that they can speed up read-modify-write operations. They redirect the write to a clean page somewhere instead of waiting for the old page to erase since erasing is slow. In essence, the flash controller moves the data to a physically different page on the drive, but from the perspective of the file system it hasn't moved.

 

Since the file system doesn't know where blocks actually are on the disk, it can't re-order them in any useful way. Thus, the fs can't defrag the disk.

 

This really isn't a problem though because ssds dont have seek latency, so it doesn't matter if blocks are contiguous or not.

Yeah basically modern OS's support TRIM, which is the defrag-like "housekeeping" functionality of the SSD, in part which you just described.

 

Older OS's like Windows XP don't support TRIM, and must be "manually optimized" using software provided by the SSD manufacturer (Samsung SSD Magician is one example). My former boss bought a couple SSD's for his Windows XP laptop. He'll probably stick with XP until the day he dies.

[eshbop]

They are fragmented by design. As long as the controller is capable, greater fragmentation = greater speeds. It's that's why higher capacity drives, with more NAND chips, are faster than smaller drives, with fewer chips. Data can be accessed more quickly when it's spread over more chips and the SSD moves data around to where it's read quickest. When seek time latency is negligible it pays to keep it fragmented. Fragmentation also means all NAND chips are written,erased&read to/from equally, rather than degrading the same sectors with repeated use.