On Thu, 17 Sep 2009, Sunil Mushran wrote: > Micah Dombrowski wrote: > > I couldn't think of anywhere else to ask such a question, and google is > > useless as I have no unique keywords. I am wondering if it is possible with > > some/any filesystems to have multiple hard links to a file, some of which > > only point to a subset of the file's data. > > > > Eg: > > firstname -> all data bytes 1 to 10 > > secondname -> bytes 3 to 10 > > thirdname -> bytes 5 to 7 > > > > This would clearly require some interesting locking of the file WRT writes, > > but it seems like it should be possible, and even easy for read-only access. > > I deal with moderately large data files (50+GB), and such a thing would be > > incredibly useful to me for pulling out interesting bits of my data without > > having to make copies of the data itself. > > > > A related method I was wishing existed would allow concatenation of files > > simply by deleting all but one hard link, and changing the remaining one to > > point to all of the original files' data as fragments. This would be great, > > as 'cat'ing together six 10GB files is pretty slow, and it seems silly to be > > copying all of that data around when I only need one actual instance of the > > full data on disk, and that instance already exists, albeit in a fragmented > > manner. > > > > Do any tools for doing this sort of thing exist? > > > > btrfs should able to handle most of this. > > http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-unstable.git;a=commitdiff;h=c5c9cd4d1b827fe545ed2a945e91e3a6909f3886 Note that currently, you can only clone a range from one file to another. It should be pretty straightforward to allow cloning from one offset to another. Or, you can work around it by cloning the range to a temporary file and then back again at a different offset. The code can also currently fail when compression is enabled and you clone a subset of the file (compressed inline extents don't get split yet). sage > > However, note that file systems operate in terms of blocks. So the start > offset would need to be block aligned. > -- > 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 > > -- 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
