Re: [PATCH 003 of 5] md: Change ENOTSUPP to EOPNOTSUPP

[Ric Wheeler <ric@emc.com>]

Molle Bestefich wrote:

> NeilBrown wrote:
>
>> Change ENOTSUPP to EOPNOTSUPP
>> Because that is what you get if a BIO_RW_BARRIER isn't supported !
>
>
> Dumb question, hope someone can answer it :).
>
> Does this mean that any version of MD up till now won't know that SATA
> disks does not support barriers, and therefore won't flush SATA disks
> and therefore I need to disable the disks's write cache if I want to
> be 100% sure that raid arrays are not corrupted?
>
> Or am I way off :-).
>
You are absolutely right - if you do not have a validated, working 
barrier for your low level devices (or a high end, battery backed array 
or JBOD), you should disable the write cache on your RAIDed partitions 
and on your normal file systems ;-)

There is working support for SCSI (or libata S-ATA) barrier operations 
in mainline, but they conflict with queue enable targets which ends up 
leaving queuing on and disabling the barriers.

ric