1. What is ``Continuous Snapshotting''?

   Continuous snapshotting is a technique to backup and recover data by creating numbers of recovery points, and users can restore files mistakenly overwritten or destroyed even the misoperation happened a few seconds ago.

2. diff command does not report any difference between file on snapshot and which on current file system.

   In some cases, diff regards two directories (or files) as identical when both their block devices and inode numbers equal.
   So, this is the matter depending on the current NILFS specification where a rw-mount and their snapshots are mounted on the same block device.
   Although we can avoid it by rewriting the diff command a bit, we think it's not preferable.
   It may take some time to eliminate the problem.

   cp command does not overwrite the current file, if source is the past file of the copy target. Please copy to temporary file, then mv it to the target name.

3. On SuSE Linux 10.0 (Kernel: 2.6.13-15-default), the iozone program terminated with a `Segmentation fault'.

   In addition, kernel may show messages "kernel BUG at fs/inode.c:252! ..." in file /var/log/messages.
   The SUSE 10 kernel is based on the 2.6.13, but some features are incorporated from newer vanilla kernels. We recommend using vanilla kernels, but if you want to use the SUSE 10 kernel, please install the kernel-source package and apply following patch.

   diff -u fs/kern_feature.h.save fs/kern_feature.h
   --- fs/kern_feature.h.save
   +++ fs/kern_feature.h
   @@ -31,6 +31,9 @@
     * Please define as 0/1 here if you want to override
     */
    
   +/* for SuSE 10.0  2.6.13-15-default kernel */
   +#define NEED_TRUNCATE_INODE_PAGES 1
   +
    /*
     * defaults dependent to kernel versions
     */
   

4. On FedoraCore 4 (Kernel: 2.6.11-1.1369_FC4smp), writing file to NILFS partition causes system hang.

   Almost same above question, default kernel of FC4 incorporates some features from newer kernels. Try following patch.

   diff -u fs/kern_feature.h.save fs/kern_feature.h
   --- fs/kern_feature.h.save
   +++ fs/kern_feature.h
   @@ -33,7 +33,7 @@
    /*
     * Please define as 0/1 here if you want to override
     */
    
   +/* for FedoraCore 4  2.6.11-1.1369_FC4smp kernel */
   +#define NEED_RWLOCK_FOR_PAGECACHE_LOCK 1
    /*
     * defaults dependent to kernel versions
     */
   

5. For Red Hat Enterprise Linux / CentOS 5.0 (Kernel: 2.6.18-8.el5), NILFS cannot be compiled.

   Almost same above question, default kernel of Red Hat Enterprise Linux 5.0 incorporates some features from newer kernels. Try following patch.

   diff -u fs/kern_feature.h.save fs/kern_feature.h
   --- fs/kern_feature.h.save	2007-07-24 09:33:11.000000000 +0900
   +++ fs/kern_feature.h	2007-08-28 15:32:40.000000000 +0900
   @@ -33,6 +33,13 @@
    /*
     * Please define as 0/1 here if you want to override
     */
   +#define	PageChecked	PageFsMisc
   +#define	SetPageChecked	SetPageFsMisc
   +#define	ClearPageChecked	ClearPageFsMisc
   +#define	NEED_MOUNT_SEMAPHORE	1
   +#define	NEED_INODE_GENERIC_IP	0
   +#define	NEED_INODE_BLKSIZE	0
   +#define	HAVE_PAGE_MKWRITE	1
    
    /*
     * defaults dependent to kernel versions
   

Send us your questions!!