> The devices are stopped at some point, that should ensure that the > caches are stable. so assuming that I have no data caches (to be written to the disk) hanging around the system; I should be able to just unplug the sata/power cable? :-} (i.e., equivalent to nice shut-down?) I always thought that there was some special os command to shuts it nicely, i.e., all confirmed within disk internal that its 32/64mb is empty before goes off... I know for raid-wb with bbu, no problems whatsoever.. Regards On Thu, Aug 4, 2011 at 19:03, Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote: > On 2011-08-04 08:58, DongJin Lee wrote: >> just adding 2c question: >> >>> On Thu, Aug 4, 2011 at 18:45, Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote: >>> That does not mean it's stable, it could just be >>> sitting in the drive write back cache. >> >> right, example with a simple hdd 2tb with some 64mb cache, so indeed, >> there's no real way to confirm that the data has been physically >> written to the mechanical platter; > > Usually any type of device that has a write back caching scheme also > supports a command to sync/flush that cache. This is what the kernel > does when you use one of the fsync() variants. > >> but as I understand when shutting down the system, all are physically >> written to the platter; so I wonder what command the os issues to the >> disk then? maybe just unmount do so? > > The devices are stopped at some point, that should ensure that the > caches are stable. > > > -- > Jens Axboe > > -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
