Why is defraging so slow?

[marsmimar]

I would say the jury is still out on defragging SSDs.

At first glance, most experts will state that SSDs do not need to be defragged. Mike Karp, Systems Management News storage columnist, pointed out that there are two kinds of SSD and that defragmenting either is not needed.

“There is no conceivable reason to defragment either. SSDs based on RAM will not be adversely affected by defragging unless your concept of defragging involves the use of a hammer,” said Karp. “Flash-based SSDs are all also unlikely to be harmed, but there is a caveat: Because the lifetime of flash memory is typically limited by the total number of writes the memory can accept, and because defragging actually does a rewrite in the process of making data contiguous, a defragmenting procedure will shorten the life of the flash memory by lessening the number of writes that the chip can accept.”

While Karp is not alone in his view of defragging’s usefulness in SSDs, there are those who think otherwise. Most notable among the supporters of defragging SSD is Diskeeper, a Burbank, Calif.-based company that offers numerous defragmentation tools for standard hard drives and storage arrays.

Gary Quan, senior software architect at Diskeeper, acknowledged that flash-based SSDs have a lifespan, and therefore shouldn’t be defragmented as often as typical hard drives. But that’s not to say he hasn’t seen benefits from defragmentation in SSDs.

“What we found out is that fragmentation can really hurt the I/O bandwidth on SSDs. There isn’t that much of a performance degradation until the files become heavily fragmented. But there may be an increase in the number of I/O operations that have to occur. That’s not where we’re seeing the degradation. We’re seeing that during write activity. When the free space is badly fragmented, the writes can see 30 to 40 percent degradation in performance,” said Quan.

Do Solid State Disks Need Defragging? - Systems Management News On The Web

Granted, this is an older article but a search for "do you need to defrag solid state drives" seems to have the community split. From what others have posted on this forum, SSDs probably won't need to be defragged as often as HDDs and it probably won't make a noticeable difference in their expected life span.

 

[Keiichi25]

Long Term Fragmentation is a problem in general, but what I think they are saying for SSDs, is that the kind of fragmentation that would cause problems with programs might not be 'noticeable' for SSDs. There is the possibility, that unlike spindle based disks, the option to place data won't be nearly as random as it is with normal hard disks due to a LACK of having to find a convenient place to put the data at a given time due to spinning of a disk. The life time of the SSD will probably have its own Read/write failure due to the fact the drive has finally reached its limit within its life time before fragmentation is an issue.

 

[techcal]

SSDs don't need conventional defrag since fragmentation does not affect sequential read/write and random read times. Infact unnecessary/inefficient defrag can use up read/write cycles of the SSD cell as has been indicated in other posts above. SSDs are known to suffer from relatively poor random write performance though IIRC.

So most SSDs can benefit from optimization of file arrangement and free space consolidation for minimizing random writes (which are slow) and increasing sequential writes. Some of the better commercial auto defraggers have add-ons that do this optimization automatically in the background.