Re: geli TRIM support

On 2014-03-21 11:53, RW wrote:
> 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.
> 
>     
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1. There is work to make a persistent L2ARC, but it is not finished yet

2. Having an L2ARC (or ZIL for that matter) on the same SSD that the
files are on, is only going to hurt. Using an L2ARC takes up more RAM,
leaving less for the primary ARC, and as was pointed out about, turns
reads into writes. Reading from the L2ARC partition is not going to be
any faster than reading from the main data partition, so I don't see the
point. Same goes for writes to a ZIL.

If your laptop has only 1 drive, an SSD, then you probably just want to
use the entire thing for the ZFS pool, rather than partitioning it to
use the advanced features that are meant to use SSDs when the pool is
NOT SSDs.

-- 
Allan Jude