On Mar 10, 2005 12:10 +0100, Jérôme Petazzoni wrote: > 1) Is there a way to check the size of the journal of an ext3 filesystem ? > I mean - the actually used size ; not the total size of the journal. There is no current statistics on any journal usage (though it would be nice to have this). Knowing how much space there currently is in the journal, some sort of average of the free journal space (e.g. abs(head-tail) as each new handle started), how often the journal was totally full and had to be flushed, etc. This would go a long way to telling a user and the ext3 developers how large a journal is needed under their workload. Currently Lustre just creates very large (400MB) journals on all of the filesystems because we know that a large journal improves the performance dramatically, but we have never done the trial+error approach of finding the "optimal" size. > 2) Would it be difficult to implement "freeze" of ext3 filesystem - that > is, blocking all I/O to the filesystem until it's "unfrozen" (XFS can do > that), for two purposes : > A/ allowing "freezing" in a clean state, to allow clean snapshotting > B/ allowing "freezing" while moving a SCSI disk or a network-connected > disk without umounting filesystem This is already done, and is used by the LVM/device mapper subsystem to do snapshots of the filesystem. However, I'm not sure if there is a user-space API to access this. > 3) Is it possible to allow data to stay in the journal for a very long > time ? > Rationale : for laptops with a lot of memory and some solid-state > memory, this would allow to shutdown the hard disk (if all read data is > in the cache, and all written data goes to the log on the solid-state disk). Yes, this can be done (I think) by tuning the journal flush time and having a large enough journal to avoid filling it up. However, I don't think this would be practical because the only common way to do this would be e.g. flash memory and the heavy usage of the journal would quickly wear out such devices, and it would also be slow. Cheers, Andreas -- Andreas Dilger http://members.shaw.ca/adilger/ http://members.shaw.ca/golinux/ _______________________________________________ Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
