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Re: xfs: very slow after mount, very slow at umount

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: xfs: very slow after mount, very slow at umount
From: david@xxxxxxx
Date: Fri, 28 Jan 2011 11:26:00 -0800 (PST)
Cc: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>, Alex Elder <aelder@xxxxxxx>, Mark Lord <kernel@xxxxxxxxxxxx>
In-reply-to: <20110128135629.GX21311@dastard>
References: <4D40C8D1.8090202@xxxxxxxxxxxx> <20110127033011.GH21311@dastard> <4D40EB2F.2050809@xxxxxxxxxxxx> <4D418B57.1000501@xxxxxxxxxxxx> <alpine.DEB.2.00.1101271040000.31246@xxxxxxxxxxxxxxxx> <4D419765.4070805@xxxxxxxxxxxx> <4D41CA16.8070001@xxxxxxxxxxxxxxxxx> <alpine.DEB.2.00.1101271209370.17579@xxxxxxxxxxxxxx> <4D42056E.2050505@xxxxxxxxxxxxxxxxx> <alpine.DEB.2.00.1101271730030.17579@xxxxxxxxxxxxxx> <20110128135629.GX21311@dastard>
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)
On Sat, 29 Jan 2011, Dave Chinner wrote:

On Thu, Jan 27, 2011 at 06:09:58PM -0800, david@xxxxxxx wrote:
On Thu, 27 Jan 2011, Stan Hoeppner wrote:
david@xxxxxxx 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. 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.

David  Lang

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