On Wed, Sep 22, 2010 at 12:30:58PM -0600, Neil Perrin wrote: > On 09/22/10 11:22, Moazam Raja wrote: > >Hi all, I have a ZFS question related to COW and scope. > > > >If user A is reading a file while user B is writing to the same file, > >when do the changes introduced by user B become visible to everyone? > >Is there a block level scope, or file level, or something else? > > > >Thanks! > > Assuming the user is using read and write against zfs files. > ZFS has reader/writer range locking within files. > If thread A is trying to read the same section that thread B is > writing it will > block until the data is written. Note, written in this case means > written into the zfs > cache and not to the disks. If thread A requires that changes to the > file be stable (on disk) > before reading it can use the little known O_RSYNC flag.
That's assuming local access (i.e., POSIX semantics). It's different if NFS is involved (because of NFS' close-to-open semantics). It might be different if SMB is involved (dunno). Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
