On Sat, Jan 3, 2009 at 1:08 AM, rohit vashist <rohitvashist2kk3@xxxxxxxxx> wrote: > > > On Sat, Jan 3, 2009 at 2:51 AM, Greg Freemyer <greg.freemyer@xxxxxxxxx> > wrote: >> >> On Fri, Jan 2, 2009 at 3:34 PM, rohit vashist >> <rohitvashist2kk3@xxxxxxxxx> wrote: >> > Hi >> > >> > I went through the code of iostat.In the ninth field it gives the count >> > of >> > number of I/O,but it goes zero but it can be thought. >> > Can u specify the grounds how hard it would to be suspend all the I/O >> > currently on the device. >> > >> > Thanks >> >> I'm confused. You only need to suspend all write activity per your >> first post not all I/O, right? >> >> Are you trying to suspend write activity to the filesystem, or to the >> underlying block device (ie. hdd/dm/md devices)? > > I just need to stop all the write operations on file system i.e it can be > deviated to the request queue for a while though reads can be allowed . > >> >> In a previous thread you asked about the filesystem block device >> freeze support and seemed unhappy that it only suspended writes to the >> block device, but left the filesystem writable via temporarily holding >> data in a write cache. > > Sorry but i think that was not my thread. > >> >> But in the above you ask about how to suspend writes to the block >> device, and you already know how to do that. At least writes >> initiated by a filesystem. >> >> Please explain with more clarity where you need to suspend writes and >> why a block device freeze is not adequate. > > See i need to suspend all writes on the file system for a moment.But i can > allow all the reads to continue.That's all i need for now. >> >> Is the problem that whatever filesystem you are working with does not >> support block device freeze? Sounds to be that you are trying to perform a "filesystem block device freeze". Several filesystems support this because it is needed to relieably create snapshots. Reposting a couple messages from earlier this week on kernelnewbies: === freeze_bdev function ( fs/buffer.c) lock a filesystem and force it into a consistent state ... Above function use s_frozen flag to freez the file system ... === some confusion about userspace not being blocked by the above. === Do you understand the purpose of the freeze? It is to ensure the underlying block device is stable and consistent. I believe the primary in kernel user of freeze is device mapper (DM). DM effectively does: freeze create COW based snapshot unfreeze. Creation of a COW (copy on write) snapshot is extremely quick, so the freeze should only be in place for a very short period of time. Note that reads of the filesystem do not interfere with the above. Also, while frozen the filesystem is allowed to support a write cache, it just cannot forward the writes / inode creations / etc. down to the block device it is sitting on. === HTH Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
