USB drives, caching and sync
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From: Boudewijn Dijkstra on 18 Jan 2010 07:52 Op Mon, 18 Jan 2010 13:38:20 +0100 schreef Noob <root(a)127.0.0.1>: > Paul Keinanen wrote: >> On Fri, 15 Jan 2010 08:44:33 +0000, Nobody wrote: >> >> Of course, writing to the file and fsyncing should be done from the same >> thread. > > OK, but many threads may be writing to the disk "at the same time" but not to the same file I hope? > i.e. concurrently, whereas vfs_sync is supposed to flush everything > to disk (even data and metadata from other threads). Perhaps you're reading over the initial 'f' of fsync. -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail)
From: Noob on 19 Jan 2010 07:37 Boudewijn Dijkstra wrote: > Noob wrote: > >> Paul Keinanen wrote: >> >>> Of course, writing to the file and fsyncing should be done from the same thread. >> >> OK, but many threads may be writing to the disk "at the same time" > > but not to the same file I hope? Each thread writes to its own file, in its own directory. >> i.e. concurrently, whereas vfs_sync is supposed to flush everything >> to disk (even data and metadata from other threads). > > Perhaps you're reading over the initial 'f' of fsync. I don't quite understand. I think you're saying fsync works on a file, whereas sync works on an entire volume, but I'm not getting your point. On my system, fsync is called vfs_fflush, and I've tried calling it right before closing a file, but the OS still runs fsck when I replug the drive. Calling sync seems to make the OS happy. Regards.
From: Boudewijn Dijkstra on 19 Jan 2010 08:03 Op Tue, 19 Jan 2010 13:37:25 +0100 schreef Noob <root(a)127.0.0.1>: > Boudewijn Dijkstra wrote: >> Noob wrote: >> >>> i.e. concurrently, whereas vfs_sync is supposed to flush everything >>> to disk (even data and metadata from other threads). >> >> Perhaps you're reading over the initial 'f' of fsync. > > I don't quite understand. > > I think you're saying fsync works on a file, whereas sync works on an > entire volume, but I'm not getting your point. Paul asked about fsync, but your reply only mentioned other functions. That was my point. > On my system, fsync is called vfs_fflush, Says who? fsync and fflush are supposed to be different things, with different purposes and differing behaviour. > and I've tried calling it > right before closing a file, but the OS still runs fsck when I replug > the drive. Calling sync seems to make the OS happy. -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail)
From: Noob on 19 Jan 2010 09:56 Boudewijn Dijkstra wrote: > Noob wrote: > >> On my system, fsync is called vfs_fflush, > > Says who? fsync and fflush are supposed to be different things, with > different purposes and differing behaviour. In the OS I'm using, there's no fsync, and the documentation for fflush states: "vfs_fflush() writes any outstanding data (and metadata) for this file to the physical device." vfs_fflush is closer to POSIX fsync than to POSIX fflush, don't you agree? Reference for myself: http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html http://www.opengroup.org/onlinepubs/009695399/functions/fflush.html Regards.
From: Boudewijn Dijkstra on 19 Jan 2010 11:28
Op Tue, 19 Jan 2010 15:56:41 +0100 schreef Noob <root(a)127.0.0.1>: > Boudewijn Dijkstra wrote: >> Noob wrote: >> > vfs_fflush is closer to POSIX fsync than to POSIX fflush, don't you > agree? It is not about what is closer, it is about what works for you. And since your FS implementation is clearly unequal to POSIX, I believe that only people familiar with it can help you further. -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail) |