On Mon, Feb 13, 2012 at 03:50:36PM +0100, Alex Samorukov wrote: > On 02/13/2012 02:28 PM, Gary Palmer wrote: > >>> > >>>>Yes. But it will nit fix non-cached access to the disk (raw) devices. > >>>>And > >>>>this is the main reason why ntfs-3g and exfat are much slower then > >>>>working > >>>>on Linux. > >>>But _that_ can be fixed with the appropriate application of a sensible > >>>caching layer. > >>With every application? :) Are you know anyone who wants to do this? At > >>least for 3 fuse filesystems. > >The filesystem is the *BEST* place to do caching. It knows what metadata > >is most effective to cache and what other data (e.g. file contents) doesn't > >need to be cached. Any attempt to do this in layers between the FS and > >the disk won't achieve the same gains as a properly written filesystem. > >e.g. in a UFS implementation the disk layer may see a lot of I/Os for > >blocks, not necessarily sequential, as a program lists a directory and > >stats > >all the files which pulls in the inode tables. The filesystem knows that > >it > >needs the inode tables and is likely to need not only the current inode > >table > >disk block but subsequent ones also, and instead of requesting the disk > >sector > >that it needs to service the immediate stat(2) request but maybe the next > >few > >also. Without that insight into whats going on it is difficult to see how > >a > >highly effective cache could be done at the geom layer. > I think we are playing in a "captain obvious". > > I have nothing against statement that FS is a "best place for caching". > Also - i am absolutely sure that its better to have kernel space fs > driver then FUSE one. > > But unfortunately there is no kernel space driver for the exfat, kernel > driver for ntfs is ugly and buggy (and r/o) and i don`t think that > anyone is going to change this. > > And i really don`t understand why are you trying to tell that it cannot > be effective when its so easy to proof that it can. Just try this with > fuse based filesystems in Linux, and you will get speed compared to > underlying device (especially on relatively slow USB devices). Then try > the same code on FreeBSD to see how ugly things are. > > And yes, in ideal world ever fs needs to have good written cache > implementation and kernel should not care about caching raw devices at > all. But as i mentioned before - there is no kernel-space drivers with a > good cache implementation for this 2 widely used systems (and probably > not only). Linux is a good example that device-level caching works, and > works fine.
Please re-read my message. At no time did I say that caching below the FS could not provide speed improvements. I said it could not be as effective as a properly implemented filesystem. I'm sure if you throw memory at it, a geom layer cache can provide substantial speed ups. However I strongly suspect that a proper FS cache would provide a better memory/hit ratio than a geom layer cache. Gary _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
