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Solid State Drives Tested With TRIM Support
Vigile writes "Despite the rising excitement over SSDs, some of it has been tempered by performance degradation issues. The promised land is supposed to be the mighty TRIM command — a way for the OS to indicate to the SSD a range of blocks that are no longer needed because of deleted files. Apparently Windows 7 will implement TRIM of some kind but for now you can use a proprietary TRIM tool on a few select SSDs using Indilinx controllers. A new article at PC Perspective evaluates performance on a pair of Indilinx drives as well as the TRIM utility and its efficacy."
I finally got the opportunity to test out SSDs this year. There may be the odd teething problem to get over, but in my mind there is no market in the future for mechanical drives except maybe as cheap low-speed devices for storing non-critical information... in much the same way as tape drives were used a few years ago.
Even the best consumer-level SSDs like the Intel x-25m/e use a volatile RAM cache to speed up the writes. In fact, with the cache disabled, random write IOPS drops to about 1200, which is only about three or four times as good as a 15k 2.5" drive. The more expensive truly-enterprise SSD drives which don't need a volatile write cache cost at LEAST $20/GB, so the $/(safe random write iop) ratio is actually still pretty close, and cheap SATA drives may actually be even on that metric as the fast enterprise SSDs. Granted, this shouldn't be the case in a year, but that's where it is right now. (Also, the performance-per-slot is a lot higher for SSDs, which can translate into different $ and power and space savings.)
Because, basically, flash drives are laid in levels.
When you delete, you simply map logical space as free.
If you go to use that free space later, you find that area, and drop shit into it. It's I dunno, a 32 KB block of memory called a page. If the page is full (to the point where you can't fit your new shit) of "deleted" files, you first need to write over those deleted files, then write your actual data.
If the logical space is full with good, fragmented (with deleted files interspersed) files, you need to read out to memory, reorder the living data and remove the deleted data, add in the full page back.
Think of it as having a notebook.
You can write to 1 page at a time, only.
Page 1 write
Page 2 write
Page 3 write
Page 2 delete
Page 2 write (still space)
Page 2 write (not enough space, write to page 4 instead)
Page 2 delete
Page 2 write (not enough space, no more blank pages, read page 2 and copy non-deleted shit to scratch paper, add new shit to scratch paper, cover page 2 in white out, copy scratch paper to whited-out page 2)
Very interesting, I assumed the problem was similar to fragmentation and wondered why nobody compared it as such.
Now, your explanation makes things much more clearer, the global problem is amplified by the additional problem you described.
Now would implementing the logic to control the SSD entirely at the OS/FS level be much slower than implementing it in silicon in the SSD itself ?
As you said, I now understand that the OS/FS would now have to be aware of the underlying media ;-)
Everything I write is lies, read between the lines.