-----Original Message----- From: linux-lvm-bounces@redhat.com [mailto:linux-lvm-bounces@redhat.com] On Behalf Of Greg Freemyer Sent: Monday, March 16, 2009 5:36 PM To: LVM general discussion and development Subject: Re: fsync() and LVM On Mon, Mar 16, 2009 at 5:17 PM, Les Mikesell <lesmikesell@gmail.com> wrote: > Greg Freemyer wrote: >> >>>> Those are some very significant subsystems. I have to believe >>>> filesystems have another way to implement fsync if barriers are not >>>> supported in the stack of block susbsystems. >>> >>> If you can't get the completion status from the underlying layer, how can >>> a >>> filesystem possibly implement it? >> >> Barriers is a specific technology and they were just implemented in >> linux around 2005 I think. (see documentation/barriers.txt) >> >> Surely there was a mechanism in place before that. > > I'm not sure that's a reasonable assumption. > >>>> Maybe this discussion needs to move to a filesystem list, since it is >>>> the filesystem that is responsible for making fsync() work even in the >>>> absence of barriers. >>> >>> I though linux ended up doing a sync of the entire outstanding buffered >>> data >>> for a partition with horrible performance, at least on ext3. >> >> Yes, I understand fsync is horribly slow in ext3 and that may be the >> reason. Supposedly much better in ext4. Still if a userspace app >> calls fsync and in turn the filesystem does something really slow due >> to the lack of barriers, then this conversation should be about the >> poor performance of fsync() when using lvm (or mdraid, or drdb), not >> the total lack of fsync() support. > > I haven't seen anyone claim yet that there is support for fsync(), which > must return the status of the completion of the operation to the > application. If it does, then the discussion could turn to performance. > > -- > Les Mikesell > lesmikesell@gmail.com Is your specific interest to ext3? If so, I suggest you post a question there along the lines of: Device Mapper does not support barriers if more than one physical device is in use by the LV. If I'm using ext3 on a LV and I call fsync() from user space, how is fsync() implemented. Or is it not? The ext4 list is <linux-ext4@vger.kernel.org>. I see some ext3 stuff posted there, or it may have its own list. Greg -- ======================================== So what happens if there is a database implemented directly on a Logical Volume, not File System involved at all? Should the fsync man page describe what happens when used on each type of File System, Logical Volume, disk partition and /or combination? ----- Thanks: Jack Allen _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
