Heads up

[Warner Losh]

On Thu, Apr 14, 2016 at 7:22 PM, Alfred Perlstein <bright at mu.org> wrote:

>
>
> On 4/14/16 3:42 PM, Warner Losh wrote:
>
>> The CAM I/O scheduler has been committed to current. This work is
>> described
>> in https://people.freebsd.org/~imp/bsdcan2015/iosched-v3.pdf though the
>> default scheduler doesn't change the default (old) behavior.
>>
>> One possible issue, however, is that it also enables NCQ Trims on ada
>> SSDs.
>> There are a few rogue drives that claim support for this feature, but
>> actually implement data corrupt instead of queued trims. The list of known
>> rogues is believed to be complete, but some caution is in order.
>>
>> Yowch...
>
> With data at stake wouldn't a whitelist be better along with a tool for
> testing it?
>
> Example, you have whitelist and blacklist, if the device isn't on either
> list you output a kernel message and suggest they run a tool to "test" the
> controller and report back the findings?


The only way to test it is to enable it. Run it for a day or six. If your
data goes away, the drive is a lying sack. There's no tool to detect this
that I've seen. You run the NCQ trim, it works. You do it again, it works
again. After a while, if you have a bad drive model, bad things happen that
are drive model specific.

Did I mention that the black list matches Linux's black list and that only
a tiny number of drive models lie. I guess I didn't.

I am thinking of adding a tunable to turn it off though for people that are
paranoid.

Warner