Following the announcement on lkml, I have started using ext3 on one of my servers. Since the server in question is a farily security-sensitive box, my /usr partition is mounted read only except when I remount rw to install packages. I converted this partition to run ext3 with the mount options "nodev,ro,data=writeback,defaults" figuring that when I need to install new packages etc, that I could just mount rw as before and that metadata-only journalling would be ok for this partition as it really sees very little write activity. When I try to remount it r/w I get a log message saying: Jul 27 09:54:29 henry kernel: EXT3-fs: cannot change data mode on remount ...even if I give the full mount option list (including data=writeback) with the remount instruction. I can, however, remount it as ext2 read-write, but when I try to remount as ext3 (even read only) I get the same problem. Wierdly, "mount" lists it as being still an ext3 partition even though it has been remounted as ext2. I can't umount /usr because kjournald is currently listed as using the partition. The box in question is more-or-less RedHat 7.1, with ext3-2.4-0.9.4, kernel 2.4.7 and with the following relevant package versions: mount-2.11g-4 util-linux-2.11f-3 e2fsprogs-1.22-2 ...all from rawhide rpms. I'm going to try one of the partitions mounted "data=ordered" to see if I see the same sort of thing. Sean
Sean writes:> servers. Since the server in question is a farily security-sensitive box, my > /usr partition is mounted read only except when I remount rw to install > packages.If it is a security-sensitive box, you need to at least use data=ordered or data=journal. Using data=writeback allows the possibility that after a crash one user might be able to read data from deleted files of another user (note that reiserfs currently only runs the equivalent of data=writeback).> When I try to remount it r/w I get a log message saying: > Jul 27 09:54:29 henry kernel: EXT3-fs: cannot change data mode on remount > > ...even if I give the full mount option list (including data=writeback) with > the remount instruction.You _could_ leave out the data=writeback from /etc/fstab (default is ordered), and you will be able to remount OK. Also, Andrew made a patch which allowed you to specify the data= mode on remount, as long it is the same.> I can, however, remount it as ext2 read-write, but when I try to remount as > ext3 (even read only) I get the same problem.You can't change filesystem types via remount (ext2 and ext3 are different filesystem drivers). In the future, you might be able to use the ext3 driver to mount a filesystem in totally unjournaled (ext2) mode. Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
> > Agreed, and for most workloads data=ordered will have very little > > performance difference from data=writeback. > > Yup. I agree with you both. My primary motivation for using that > option was so that I could test them all. Since this partition gets > very little r/w usage, and that is quite controlled, I thought > writeback would be ok as a test. > > SeanI ran Postmark (http://www.netapp.com/tech_library/3022.html) which is a benchmark by Netapp to demonstrate fs performance in ephermeal small files. Hardware: P3-450/256MB with 2 20GB IDE disks attached to a 3ware Escalade 6200 in RAID-1 configuration Postmark ran on local filesystems. Ext3 partition was 4 GB ext2 partition was 4.5GB a) Ext3 Writeback mode b) Ext3 Ordered mode c) Ext2 Parameters used for postmark were set size 1024 20480 set subdirectories 100 set number 5000 set transactions 50000 set read 8192 set write 8192 set bias read 10 set bias create 5 In this workload, ordered mode is much slower than writeback -- Yusuf Goolamabbas yusufg@outblaze.com