Re: Some very basic questions

[Ric Wheeler <rwheeler@redhat.com>]

Avi Kivity wrote:
> 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.
>
Depends on your workload, I have measured (back at Centera) a 
significant win for mixed read/write as well (at least 20%) depending on 
file size.

>> 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.
>

Won't ever happen, no one wants to lose 50% of their performance :-)

ric