Re: Some very basic questions

[Avi Kivity <avi@redhat.com>]

Tejun Heo wrote:
> For most SATA drives, disabling write back cache seems to take high
> toll on write throughput.  :-(
>
>   

I measured this yesterday.  This is true for pure write workloads; for 
mixed read/write workloads the throughput decrease is negligible.

> As long as the error status is sticky, it doesn't have to hold on to
> the data, it's not gonna be able to write it anyway.  The drive has to
> hold onto the failure information only.  Yeah, but fully agreed on
> that it's most likely dependent on the specific firmware.  There isn't
> any requirement on how to handle write back failure in the ATA spec.
> It wouldn't be too surprising if there are some drives which happily
> report the old data after silent write failure followed by flush and
> power loss at the right timing.

I got flamed for this on another list, but let's disable the write cache 
and live with the performance drop.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.