linux-kernel - Re: xfs: very slow after mount, very slow at umount

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Message-ID: <20110129054021.GB21311@dastard>
Date:	Sat, 29 Jan 2011 16:40:21 +1100
From:	Dave Chinner <david@...morbit.com>
To:	david@...g.hm
Cc:	Stan Hoeppner <stan@...dwarefreak.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com,
	Christoph Hellwig <hch@...radead.org>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	Alex Elder <aelder@....com>, Mark Lord <kernel@...savvy.com>
Subject: Re: xfs: very slow after mount, very slow at umount

On Fri, Jan 28, 2011 at 11:26:00AM -0800, david@...g.hm wrote:
> On Sat, 29 Jan 2011, Dave Chinner wrote:
> 
> >On Thu, Jan 27, 2011 at 06:09:58PM -0800, david@...g.hm wrote:
> >>On Thu, 27 Jan 2011, Stan Hoeppner wrote:
> >>>david@...g.hm put forth on 1/27/2011 2:11 PM:
> >>>
> >>>Picking the perfect mkfs.xfs parameters for a hardware RAID array can be
> >>>somewhat of a black art, mainly because no two vendor arrays act or perform
> >>>identically.
> >>
> >>if mkfs.xfs can figure out how to do the 'right thing' for md raid
> >>arrays, can there be a mode where it asks the users for the same
> >>information that it gets from the kernel?
> >
> >mkfs.xfs can get the information it needs directly from dm and md
> >devices. However, when hardware RAID luns present themselves to the
> >OS in an identical manner to single drives, how does mkfs tell the
> >difference between a 2TB hardware RAID lun made up of 30x73GB drives
> >and a single 2TB SATA drive? The person running mkfs should already
> >know this little detail....
> 
> that's my point, the person running mkfs knows this information, and
> can easily answer questions that mkfs asks (or provide this
> information on the command line). but mkfs doesn't ask for this
> infomation, instead it asks the user to define a whole bunch of
> parameters that are not well understood.

I'm going to be blunt - XFS is not a filesystem suited to use by
clueless noobs. XFS is a highly complex filesystem designed for high
end, high performance storage and therefore has the configurability
and flexibility required by such environments. Hence I expect that
anyone configuring an XFS filesystem for a production environments
is a professional and has, at minimum, done their homework before
they go fiddling with knobs. And we have a FAQ for a reason. ;)

> An XFS guru can tell you
> how to configure these parameters based on different hardware
> layouts, but as long as it remains a 'back art' getting new people
> up to speed is really hard. If this can be reduced down to
> 
> is this a hardware raid device
>   if yes
>     how many drives are there
>     what raid type is used (linear, raid 0, 1, 5, 6, 10)
>
> and whatever questions are needed, it would _greatly_ improve the
> quality of the settings that non-guru people end up using.

As opposed to just making mkfs DTRT without needing to ask
questions?

If you really think an interactive mkfs-for-dummies script is
necessary, then go ahead and write one - you don't need to modify
mkfs at all to do it.....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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