David Kanter (dkanter@realworldtech.com) on 1/19/11 wrote:
>
>It may have been true in the past, but if you look
>at their products today, there are a lot of software
>deficiencies that impact performance.
>Perhaps the most glaring is the lack of TRIM support in
>OS X - in a company where most of their notebooks are
>using SSDs.

You have bought the whole TRIM story hook, line and sinker.

It's bogus. There is currently absolutely no reason to
support TRIM, not on SSD's, not on anything else. The whole
feature is totally broken.

The fact is, any SSD worth anything should work perfectly
fine without trim, and if you need trim to get it back to
good performance, you should just ditch the SSD entirely.

The whole "SSD's need TRIM" support was a bedtime story for
gullible morons. The same morons who also bought the "SSD's
need big IO and natural alignment" story that came out a
couple of years before that.

The fact is, SSD's had seriously buggy garbage collection.
TRIM was a workaround for an SSD firmware bug, nothing
less, and most definitely nothing more. Yes, yes, it can
make a difference, but it's not at all the magical fairy
dust that people have claimed it was. The real solution
was always to just fix the performance bugs in the bad GC
that SSD's did.

More specifically, TRIM is also incredibly buggy, and slow
on certain drives. So doing TRIM in the OS is dangerous,
and is likely to result in totally unacceptable performance
if it's used on-line (ie when removing files). And you also
raise your risk for hitting those drive-bricking bugs, so
it's doubly dangerous.

In fact, even when it's not really slow (and when it's not
buggy), it still makes a normal file deletion much more
expensive, since normally you'd just throw the blocks away
without doing any IO at all. Doing even a fast TRIM is thus
infinitely more expensive.

Finally, the whole saga has been further complicated by
historically bad specifications ("does it leave the data
in a known state") and by the fact that certain uses really
need the TRIM area to be really big and really aligned (ie
the whole non-SSD RAID use of TRIM wants it to cover whole
stripes, so you want TRIM commands to be naturally aligned
and megabytes in size).

End result: nobody sane enables TRIM by default, and it's
almost inevitably a total marketing point. And in reality,
you'd want it to be an off-line feature, ie something akin
to doing a defrag event, rather than something you do as
part of a normal filesystem operation.

Maybe the above will change eventually, but right now
TRIM is totally oversold, and totally pointless. Just don't
even bother with it. Do your SSD comparisons after you've
done lots of random writes, and expect that in real life
the time when an SSD can optimize its GC i when you do nice
large file writes. Not when you TRIM things.

And even _if_ TRIM becomes relevant (and I doubt it ever
really will - good GC makes it largely pointless), it just
won't be a huge deal.

Repeat after me: if your disk manufacturer talks about
how you need to TRIM the drive, they're cutting some corners
that you do NOT want to be cut. Buy another drive.

Linus