Linus Torvalds wrote:
>
> On Thu, 11 May 2000, Jeff V. Merkey wrote:
> >
> > And one more thing. I have grabbed Steve Dodd's NTFS code, and I am
> > implementing a fully featured NTFS implementation on Linux. I've got
> > some bad news for you here, without the ability to post variable length
> > asynch IO requests, as are supported in Windows 2000, performance of
> > Linux NTFS vs. Native Windows 2000 NTFS will SUCK WIND and perform
> > poorly. Their entire AIO architecture is built on the concept of "file
> > runs" of variable lengths for R/W IO, and most of the performance tricks
> > in native NTFS are heavily dependent on this capability.
>
> Note that what you can always do is actually very simple:
> - _always_ use a sector size of 512 bytes.
> - allocate 8 sectors per 4kB page
> - fill in the sector numbers appropriately: if you have a 2kB "run", then
> you just fill in sector numbers X, X+1, X+2 and X+3 on the four buffer
> heads in question.
> - the ll_rw_block logic will all coalesce the writes back again, so the
> IO should still be done in 2kB blocks. But you'd have the option of
> just writing 512 bytes of them if you wanted to.
>
> Note that the 512-byte sector is basically forced upon us by hardware.
> There's nothing we can do about that in software, so the above should be
> able to handle all cases that hardware can do for us reasonably.
>
> (And yes, it _will_ use slightly more CPU time, no question about that.
> However, most of the common operations are done on pages rather than on
> the buffers that are used to fill in the pages or write them back, so many
> of the higher-level IO abstractions won't even know the difference).
>
> You can do funky stuff like changing the sector numbers etc on the fly
> too, without the upper layers caring. Of course, you'd better do this when
> you own the buffer head lock, because otherwise it might be in the middle
> of a write-out or something like that, and you sure as h*ll don't want to
> confuse the device drivers with changing the sector number from underneath
> them ;)
Linus,
Cool. I will try to have this out in early form mid-summer. I am also
adding support for W2K partitions. I will implement it and when I've
got some good numbers, I'll post them. For now, so folks are aware,
they should still forward NTFS bugs on the current code to Steve Dodd,
as the new driver is being completely re-implemented from scratch --
folks should send them to Steve until I've got something decent up to
hand off to him.
NTFS does require 512-bytes blocks by default for Linux (very astute
that you already are aware of this fact) since some file runs actually
live INSIDE the MFT for small files, and are not guaranteed to be
aligned on 1024-2048-4096 block boundries.
:-)
Jeff
>
> Linus
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