iz (i@z.x) on 1/26/11 wrote:
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>Ricardo B (ricardo.b@xxxxx.xx) on 1/26/11 wrote:
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>>Michael S (already5chosen@yahoo.com) on 1/25/11 wrote:
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>>>It seems to me that it also useless when
>>>a) FS manages free logical blocks in LIFO manner (which seems to be the only logical option anyway).
>>
>>Any case where the FS favors reuse of logical blocks will tend to make TRIM useless.
>>I suspect it doesn't really matter the order, as long as the FS favors LBA re-use.
>
>Yeah, as long as enough untouched disk space is available. TRIM is useful when
>the disk got full, but a lot of space got available again. Then it's good to tell
>the SSD about it, instead of just overwriting.

The matter is even worse than you are just described. If the disk was 98% full, and after deletion/backups/etc 50% of that space has been freed, not using TRIM would mean that you are cutting the life span of the storage media by a non-trivial factor. (Suppose the SSD has 10% space on top of the size it reports to the OS. Not using TRIM after the filesystem data dropped from 98% to 50%: the SSD uses approximately 10% of the internal disk space for allocation. Proper use of TRIM: the SSD has approximately 60% of space for internal use. 60/10=6. By improper use of TRIM, you would reduce the lifetime of the disk by a factor of 6, in this particular scenario.)

Linus is wrong in saying that "TRIM is optional, the SSD GC can do without TRIM" and "TRIM is oversold". It is not oversold. SSDs *cannot* function reliably without TRIM for long periods of time, neither can they function at peak performance without TRIM. That said, TRIM is a tool, it needs to be used properly in order to be an effective solution.

I am sure this fact was discussed on multiple places already. So, I don't know what is the fuzz here about people not understanding what is TRIM for and why it is essential to properly use it.

Message to Linus:

And no, my dear Linus, the OS *cannot* out of its free will choose the strategy "do not use TRIM" or "turn it off by default". There are many people out there who will format the disk only once (or at most only a couple of times) per the lifetime of the disk. I am one such person, and you Linus are such a person as well. Due to this reason, as well as other reasons that shouldn't be ignored by the OS developers, it is *imperative* for the OS to implement the right behavior in order to extend the lifetime of the disk and to maintain a good performance level. An OS that does not care about this is not a good OS (politely said).