Messages in this thread | | | Date | Sun, 18 Sep 2005 07:23:01 +0200 | From | Willy Tarreau <> | Subject | Re: Eradic disk access during reads |
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On Sun, Sep 18, 2005 at 07:16:46AM +0300, Al Boldi wrote: > Willy Tarreau wrote: > > On Sat, Sep 17, 2005 at 01:32:53PM +0300, Al Boldi wrote: > > > Willy Tarreau wrote: > > > > On Sat, Sep 17, 2005 at 07:26:11AM +0300, Al Boldi wrote: > > > > > Monitoring disk access using gkrellm, I noticed that a command like > > > > > > > > > > cat /dev/hda > /dev/null > > > > > > > > > > shows eradic disk reads ranging from 0 to 80MB/s on an otherwise > > > > > idle system. > > New synonym: eradic=erratic :)
I've noticed from the first mail too :-)
> > Denis' tool seems clearly more suited to analyse your problem. > > The problem seems to be a multi-access collision in the queue, which forces a > ~50% reduction of thruput, which recovers with another multi-access > collision. Maybe?!
do you have anything else connected to the same controller ? I've encountered a problem a long time ago with SATA drives (it was around 2.4.25, with the beginning of SATA support), where I could not use RAID on my drives because simultaneous accesses to the drives was not possible. I then realized that every time I accessed a drive during a read from or a write to another one would stall. I don't remember if CDROM access caused the same trouble. This was with a SATA-patched ata-piix driver, but fortunately this is fixed by now.
Regards, Willy
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