On Wed, Dec 2, 2015 at 10:30 PM, Phil Turmel <philip@xxxxxxxxxx> wrote: > On 12/02/2015 09:51 PM, Dallas Clement wrote: >> On Wed, Dec 2, 2015 at 8:38 PM, Phil Turmel <philip@xxxxxxxxxx> wrote: >>> On 12/02/2015 09:33 PM, Dallas Clement wrote: >>> >>>> I'm not sure that the sync=1 has any effect in this case where I've >>>> got direct=1 set (for non buffered I/O). I think the sync=1 flag only >>>> matters for buffered I/O. I really shouldn't be setting that flag at >>>> all. >>> >>> It's substantially different from direct=1. O_DIRECT just bypasses the >>> kernel's caches. O_SYNC flushes the file data and filesystem metadata, >>> and kills the device caches and queues. >> >> Isn't O_SYNC only applicable for buffered I/O or going through the >> kernel caches? If I'm using O_DIRECT, seems like it should just >> ignore this flag. > > O_SYNC is orthogonal to whether the kernel caches are involved. It is > about ensuring that data *and* metadata are safely written all the way > to permanent media. > > Phil Okay, that was my original intent, i.e. to avoid caching and buffering as much as possible so that I could get a feel for true throughput capability of the RAID device and the disks. Do you think it would be better then to use sync=0 or fsync_on_close=1 for the sake of evaluating RAID write performance? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
