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SubjectRe: (fwd) Re: [RFC] mount flag "direct"
At 23:45 05/09/02, Daniel Phillips wrote:
>On Wednesday 04 September 2002 16:13, Anton Altaparmakov wrote:
> > Did you read my post which you can lookup on the below url?
> >
> > http://marc.theaimsgroup.com/?l=linux-kernel&m=103109165717636&w=2
> >
> > That explains what a single byte write to an uncached ntfs volume entails.
> > (I failed to mention there that you would actually need to read the block
> > first modify the one byte and then write it back but if you write
> > blocksize based chunks at once the RCW falls away.
> > And as someone else pointed out I failed to mention that the entire
> > operation would have to keep the entire fs locked.)
> >
> > If it still isn't clear let me know and I will attempt to explain again in
> > simpler terms...
>
>Anton, it's clear he understands the concept, and doesn't care because
>he does not intend his application to access the data a byte at a time.
>
>Your points are correct, just not relevant to what he wants to do.

Daniel,

The procedure described is _identical_ if you want to access 1TiB at a
time, because the request is broken down by the VFS into 512 byte size
units and I think I explained that, too. And for _each_ 512 byte sized unit
of those 1TiB you would have to repeat the _whole_ of the described
procedure. So just replace 1 byte with 512 bytes in my post and then repeat
the procedure as many times as it takes to make up the 1TiB. Surely you
should know this... just fundamental Linux kernel VFS operation.

It is not clear to me he understands the concept at all. He thinks that you
need to read the disk inode just once and then you immediately read all the
1TiB of data and somehow all this magic is done by the VFS. This is
complete crap and is _NOT_ how the Linux kernel works. The VFS breaks every
request into super block->s_blocksize sized units and _each_ and _every_
request is _individually_ looked up as to where it is on disk.

Each of those lookups requires a lot of seeks, reads, memory allocations,
etc. Just _read_ my post...

Please, I really wouldn't have expected someone like you to come up with a
statement like that... You really should know better...

Best regards,

Anton


--
"I've not lost my mind. It's backed up on tape somewhere." - Unknown
--
Anton Altaparmakov <aia21 at cantab.net> (replace at with @)
Linux NTFS Maintainer / IRC: #ntfs on irc.openprojects.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/

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