On Mon, Sep 04, 2006 at 11:01:20PM -0400, Ian Turner wrote:

| On Saturday 02 September 2006 16:21, Phil Howard wrote:
| > It would not need to be separate for each OS.  The idea of using a
| > partition table isn't even the only approach.
| 
| The tradeoff here is that if you don't use real partitions, then you (again) 
| need this tool for restore. At present the only thing you need for restore is 
| gzip and tar or dump. Even with raw partitions, that would continue to be the 
| case, but as soon as you introduce an Amanda-specific blocking format, that 
| would no longer be the case. Performance advantages might make that 
| worthwhile, but then again the same effort applied elsewhere could probably 
| yield equal improvements without the sacrifice.

If all that is written is tar format, nothing more needs to be added.
The tar format can be handled as a stream, disregarding blocks (though
I don't know if Amanda preserves that).  I do periodically write tar
directly to disk partitions (and read it back).  I've also done this
with DV format video, but that's another matter.


| > FYI, I was benchmarking some disk writing for an unrelated purpose
| > yesterday and found that in Linux 2.6 using the O_DIRECT option when
| > opening a device to write on a disk raw (even a partition) results in much
| > faster writing. Writing raw already beats writing through a filesystem. 
| > Raw with O_DIRECT is much faster than raw without.  If someone does decide
| > to write a driver for raw disk support, I suggest having its implementation
| > test for support for the O_DIRECT option, and use it where possible.  It
| > does have some size, offset, and alignment requirements that vary by OS.
| 
| This is an interesting idea, and certainly worth pursuing. I'd be interested 
| in seeing your data.

I didn't keep any stats, or really do it scientifically.  Someone that wants
to should probably control for a lot of the variables that influence it.
But I do recall the speed improvement is about 25% to 30%.  I suspect much
of that is OS work bypassed with O_DIRECT.

-- 
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| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
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