UFS2 and SSDs

[Kip Macy]

On Wed, May 13, 2009 at 7:31 AM, Ivan Voras <ivoras at freebsd.org> wrote:
> Thomas Hurst wrote:
>> * Kip Macy (kmacy at freebsd.org) wrote:
>>
>>> I accidentally bought a camera-grade SSD. Random write performance
>>> with UFS made it unusable. I ended up converting /usr to ZFS - since
>>> which time I've been very happy with performance.
>>
>> Did you try gjournal on it?  SSD's should do better with sequential
>> journal writes.
>
> My guess is that it won't matter - the issue is "small writes" not
> "sequential writes". Gjournal will issue writes as it receives them - if
> it receives a bunch of small ones, it will pass them on in the same
> form, only sequential (the drive will still see a bunch of small
> writes). This works well for mechanical drives because of rotational
> properties but does nothing to SSDs.
>
> ZFS OTOH does a great deal of buffering.


The benefits come from write-allocate - writes always end up being
some multiple of erase blocks. With FFS the drive constantly has to GC
partial blocks.


-Kip


-- 
When bad men combine, the good must associate; else they will fall one
by one, an unpitied sacrifice in a contemptible struggle.

    Edmund Burke