On 28 jan 2010, at 12.11, Björn JACKE wrote: > On 2010-01-28 at 00:30 +0100 Ragnar Sundblad sent off: >>> Are there any plans to add unwritten extent support into ZFS or any reason >>> why >>> not? >> >> I have no idea, but just out of curiosity - when do you want that? > > when you have many data streams being simultaneous written to disk over a > long time you end up with highly fragmented files. When you write to a file > with > random seeks (think of torrent) you end up with an extremely fragmented file. > When > you have a virtual disk image which "grows" over time, you will get a > fragmented disk image which affects performance bad. When you write to a file > and you want to be sure you have enough space to write all the data, even if > writing to that file takes some time, preallocation takes care the space is > yours. Threre are plenty of reasons to do preallocation. With unwritten extent > support preallocation is a cheap thing to do.
Ok, I now understand what you want, thanks! On zfs, your files will get fragmented anyway, preallocated or not, because all new data and metadata in a transaction group is written to unallocated blocks on the disk. As far as I know, there is no way to have zfs write to the same place as the data you are rewriting. /ragge _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
