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Date:      Sun, 22 Jan 2006 20:14:09 +0100
From:      "Wojciech A. Koszek" <dunstan@zsno.ids.czest.pl>
To:        Maxim.Sobolev@portaone.com
Cc:        freebsd-current@freebsd.org
Subject:   Re: [PATCH] Support for large number of md(4) disks
Message-ID:  <20060122191409.GB84400@zsno.ids.czest.pl>
In-Reply-To: <43CF22AD.3080702@portaone.com>
References:  <20060114223019.GA99634@FreeBSD.czest.pl> <43CC168D.9080708@portaone.com> <20060118082804.GC4846@FreeBSD.czest.pl> <43CF22AD.3080702@portaone.com>

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On Wed, Jan 18, 2006 at 09:25:01PM -0800, Maxim Sobolev wrote:
> Wojciech A. Koszek wrote:
> >On Mon, Jan 16, 2006 at 01:56:29PM -0800, Maxim Sobolev wrote:
> >>Hi,
> >
> >Hi Maxim,
> >
> >>IMHO there is better approach to fetch unknown amount of data from the 
> >>kernel using ioctl(2) facility. The main idea is that you allocate some 
> >>buffer of size sufficient in 95% of cases (for md(4) I think 8-16 
> >>entries are enough), attach it to some structure which has size of the 
> >>buffer as one of its members and send pointer to that structure as an 
> >>argument to ioctl(2).
[..] 
> Yes, there is a difference. I don't like your approach when you are 
> trying to win the race fixed amount of times (5) and then just bailing 
> out, asymptotic approach is better IMHO. Especially considering that 
> memory is cheap nowadays and you won't have any problems with allocating 
> space for many thousand configuration entries, even in the case when you 
> are really going to use only few of them.
> 
> Regarding you assumption that meeting the situation when total number of 
> devices changes quickly I don't quite agree. A simple script can make 
> number of md(4) devices going up/down by few hundred per second easily, 
> your approach will behave erratically in such case.
> 

I got some feedback from people who use md(4) in such cases. Looking at
bugs@ gives me a feel there is also a real need for mdconfig -l working
properly..

...this is why updated patch is here:

	http://zsno.ids.czest.pl/~dunstan/FreeBSD/mdconfig-list.3.patch

It starts with 16 entries in the user-space.
Thanks!
-- 
* Wojciech Koszek && <dunstan%zsno.ids.czest.pl>




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