Is TRIM working with gmirror?

[Karl Pielorz]

--On 12 December 2013 01:16:09 +0100 Miroslav Lachman <000.fbsd at quip.cz> 
wrote:

> Is TRIM working on gmirror?
>
> I have FreeBSD 8.4-RELEASE-p1 amd64 GENERIC machine with 2x SSDs:
...
> But there is a WARNING at boot:
>
> WARNING: /ssd_db: TRIM flag on fs but disk does not confirm that it
> supports TRIM
>
> The filesystem is classic UFS2.
>
> Is TRIM supported throught gmirror, or not?

I think 8.4 is way too old for this. I have a number of 9.2 boxes - and 
even on those, TRIM doesn't propagate through gmirror *yet* (at the time, 
which is a few months ago I seem to remember reading 'It should work soon' 
- but 9.2 doesn't appear to).

You can use gstat to show if any calls to BIO_DELETE are being made - i.e.

  gstat -d

On the systems here the 'd/s' (which afaik is 'BIO_DELETE/second') remains 
stubbornly at zero :(

The flipside is with decent SSD's these days TRIM isn't quite so 
important... Some may even argue that *not* issuing heaps of BIO_DELETE on 
the I/O channel is actually faster - so long as the SSD has time to play 
catchup and isn't pegged all the time, I think they may be right :-)

-Karl