On Mon, Dec 09, 2002 at 02:31:38PM -0800, Jason R Thorpe wrote:
>  > Hum, I think with tagged queuing, the command won't complete before
>  > data is on the media.
> 
> Are you *sure*?  I'm not certain that this is actually a requirement,

fwih on l-k, the ata spec specifies a write cache flush command, but there
are (pos) drives that ignore it. i've also read that some ata drives lie
about disabling their cache, to cheat on benchmarks.

however, i consider any drive that returns from a cache flush, or does not
disable write cache when told to, to be broken and useless for anything but
/tmp and unimportant caches.

> and I have some emperical data which suggests that its not the case.  I.e.
> I have disks where tagged queueing is being used, and write speed goes WAY
> up when the write-cache is enabled.

right, it's writeback caching. it returns cmd success right after it gets
the cmd. do you mean that ordered tags aren't being honored by some scsi
drives?

i'm not an expert on scsi (and definetly not ata). is there a write barrier
flag for cmd tags? how do ordered tags work?

-- 
Tom Vier <tmv@comcast.net>
DSA Key ID 0xE6CB97DA