In article <cajcb3foogeoiw_xgnrkovykigab+vf8jsiffiz8zgpyjrij...@mail.gmail.com>,
Andy Ruhl <acr...@gmail.com> wrote:
>On Thu, Jan 3, 2013 at 4:54 AM, Lars Heidieker
><lars.heidie...@googlemail.com> wrote:
>> On Thu, Jan 3, 2013 at 12:49 PM, Edgar Fuß <e...@math.uni-bonn.de> 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.
Actually it was the addition of:
sysctl -w vfs.wapbl.flush_disk_cache=0
and the discussion on the actual behavior of various cache flushing
commands on different types of buses and drives.
christos
