Re: disk requst queue problem

Pavel Machek (pavel@atrey.karlin.mff.cuni.cz)
Thu, 27 May 1999 13:16:33 +0200


Hi!

> When I do dd if=/dev/zero of=/dev/hda9, all other disk operations
> (including swapping) are suspended until dd terminates. The same with dd
> if=/dev/zero of=foo. I have ide disk. There's probably bad implementation
> of request queue. Something like request ages should be implemented. Has
> anyone another idea what to do with it?

Mikulas shown me and it really is problem. I was unable to ssh to our
server within _minute_ when dd ran. We tried to reproduce it on 2.0
system with scsi and it did not work. It is pretty effective DoS
attack and I think something like that happens in real life,
too. Notice that you have to _write_ on disk, reading does not work.

Pavel

-- 
The best software in life is free (not shareware)!		Pavel
GCM d? s-: !g p?:+ au- a--@ w+ v- C++@ UL+++ L++ N++ E++ W--- M- Y- R+

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