Re: WAPBL and write cacheing (was: SATA write performance problems)

[Andy Ruhl <acruhl%gmail.com@localhost>]

On Thu, Jan 3, 2013 at 4:54 AM, Lars Heidieker
<lars.heidieker%googlemail.com@localhost> wrote:
> On Thu, Jan 3, 2013 at 12:49 PM, Edgar Fuß <ef%math.uni-bonn.de@localhost> 
> wrote:
>>> Doesn't this depend on filesystem journaling?
>> Can someone please enlighten me?
>> Is it safe to use write cacheing on a SATA drive with FFS/WAPBL on it?
>
> AFAIK it depends on the drive, if it doesn't lie about the command to
> flush the cache it's safe.
> WAPBL sends such a command on commit.

So I think what you are saying is that WAPBL asks the drive to flush
it's volatile cache before the journal update is done?

There was talk a while back on some list (I don't remember if it was a
NetBSD list) that certain OS behavior (maybe not NetBSD) was flushing
cache so often that drive cache performance benefits were essentially
negated. So the drive would ignore some of the cache requests which
leaves systems using journaling vulnerable. The fail-safe was to just
turn off cache completely.

Andy