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