On Mon, May 11, 2009 at 12:53 PM, Joel Becker <Joel.Becker@xxxxxxxxxx> wrote: > On Mon, May 11, 2009 at 12:08:17PM -0500, Steve French wrote: >> Joel, >> Looking at your documentation for the new "reflink" syscall (to create >> copy-on-write files): >> http://git.kernel.org/?p=linux/kernel/git/jlbec/ocfs2.git;a=blob;f=Documentation/filesystems/reflink.txt;h=58a6b3879114c0cb591fb736152b30291037edd2;hb=c04db1c934e67337318b177688c0b882297fdd66 >> >> Have you looked at whether this is close enough to the existing (e.g. >> Windows NTFS) copy-on-write syntax/feature so that we could use it >> under Samba (and on the client side from cifs and in the future smb2). >> Windows added copy-on-write about 9 or 10 years ago and uses it >> extensively. although I have not researched enough to see what >> creating these would look like over the network. > > I didn't know NTFS had it There are lots of references to the various services that use copy on write (e.g. the "Groveler" service, which I first noticed back in Windows 2000 copy-on-write linking remote windows install images, which can be quite big, apparently saving enormous amounts of disk space, and also the "SIS" or "Single Instance Store" service which is an optional component of Windows servers, and I saw a reference to Vista using the same NTFS copy-on-write feature for some form of backup/snapshot) but this would be a better question for a Windows programmer not a Linux kernel developer :) copy-on-write links seem to be represented as "reparse points" (a type of Windows inode) with a tag "IO_REPARSE_TAG_SIS" (to distinguish it from other special purpose inodes such as symlinks, DFS referrals and junctions) http://msdn.microsoft.com/en-us/library/aa365511(VS.85).aspx Apparently they can be sent over the network based on section 2.4.35 of http://msdn.microsoft.com/en-us/library/cc232086(PROT.13).aspx -- Thanks, Steve -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
