Re: geli TRIM support

On Thu, 20 Mar 2014 19:34:04 +0000
Mike C. wrote:

> I was actually googling   about this yesterday and found no more info
> then the thread you posted.
> 
> So its seems that nothing was done related to this so far?
> 
> Which means using trim+geli is problematic.

These days SSD devices have static wear-levelling so you don't need to
maximize the number of free blocks, just maintain a small pool. You can
do that by not partitioning the whole device and leaving a few percent
unused. I'm not sure what you would do if the device had already been
written to though, if FreeBSD has a command to trim a device I don't
know what it is. You could just use Linux's hdparm from a live CD.

You should also be OK if you have a non-geli UFS partition with
sufficient free space on the same device. 

> I was using my ssd with UFS+trim+geli in my laptop. But even before
> noticing the lack of support changed my setup... since the laptop has
> both a ssd and hdd I am now using zfs+geli in the hdd. I have 2
> partitions in the ssd and I'm using it for log/cache.

I've been considering that, but I did have a couple of concerns:

1.  l2arc sounds like it would be  much less effective outside of
    servers because, AFAIK, the cache doesn't survive a reboot.

2.  the l2arc cache turns reads on the filesystem into writes to the
    SSD.