Re: Discard support

Mark Lord
2009-08-16T22:51:26Z

Theodore Tso wrote:
> On Sun, Aug 16, 2009 at 02:50:40PM -0700, Roland Dreier wrote:
>> > Well, yes and no ... a lot of SSDs don't actually implement NCQ, so the
>> > impact to them will be less ... although I think enterprise class SSDs
>> > do implement NCQ.
>>
>> Really? Which SSDs don't implement NCQ?
>
> The Intel X25-M was the first SSD to implement NCQ. The OCZ Core V2
> advertised NCQ with a queue depth of 1, but even that was buggy, so
> Linux has a black list for the that SSD:
>
> http://markmail.org/message/jvjpmcdqjwrmyl4w
>
> As far as I know, all of the SSD's using the crappy JMicron JMF602
> controllers don't support NCQ in any real way, which would includes
> most of the reasonably priced SSD's up until first half of this year.
> (The OCZ Summit SSD, which uses the Indilnx controller is an exception
> to this statement, but it's more expensive that the JMF602 based
> SSD's, although less expensive than the Intel SSD.)
>
> JMicron is trying to seek redemption with their JMF612 controllers,
> which were announced at the end of May of this year, and those
> controllers do support NCQ, and are claimed to not to have the
> disatrous small write latency problem of their '602 bretheren. I'm
> not aware of any products using the JMF612 yet, though. (According to
> reports the '612 controllers weren't going to hit mass production
> until July, so hopefully later this fall we'll start seeing products
> using the new JMicron controller.)
..

Great summary, Ted.

To add: SSDs based upon the Indilinx controller don't appear to scale
beyond an NCQ depth of about 4 or so. Whereas Intel SSDs continue to
improve with increased queue depth up to 31 on Linux.

Or at least that's what I recall from reading various SSD benchmarks
a few weeks ago here.

Cheers