HDD util is 100% - aio questions

Cristian Rusu crirus at gmail.com
Tue Feb 5 06:48:02 UTC 2013


Well, we don't have a single box, we have a few setups with large slow HDDs
and a couple of edge servers running on 1.5TB RAID SSD for actual streaming.

Right now it's stable(70% max util) as we managed to write a caching code
so basically the slow HDDs mainly feed the edges and only a few users at

The edge servers are way faster and cope with 10Gbit bandwidth so far.

I just hoped that aio is a solution for less strain in HDDs util%.

As for page cache, that is pretty useless as web-mysql boxes does just fine
in serving up to 2500 connections per second.

The main issue is around getting large videos in and out of HDDs fast.

Cristian Rusu
Web Developement & Electronic Publishing


On Mon, Feb 4, 2013 at 8:29 PM, Lukas Tribus <luky-37 at hotmail.com> wrote:

> Yes, I'm aware, thats why I told him to monitor the box carefully.
> However, async IO is not so easy to accomplish under linux, and since he is
> also using the streaming module, things can get complicated.
> I wonder if switching to FreeBSD would be a better idea to avoid the linux
> AIO limitations (as in the nginx documentation).
> Anyway, he needs to do some serious testing/thinking/spending time with
> it. Nobody will come up with the perfect configuration for him resolving
> all the issues.
> ----------------------------------------
> > Date: Mon, 4 Feb 2013 19:19:09 +0100
> > From: jgehrcke at googlemail.com
> > To: nginx at nginx.org
> > Subject: Re: HDD util is 100% - aio questions
> >
> > 64 GB of RAM might not be sufficient for keeping a significant part of
> > his video data in memory. Hence, depending on the number of concurrent
> > users and the average size of the videos Cristian wants to stream it is
> > entirely possible that caching videos in memory does not help at all. In
> > this case, he needs proper disk I/O settings.
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