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

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Date:	Thu, 27 Jan 2011 15:24:25 -0500
From:	"John Stoffel" <john@...ffel.org>
To:	Mark Lord <kernel@...savvy.com>
Cc:	Justin Piszcz <jpiszcz@...idpixels.com>,
	Stan Hoeppner <stan@...dwarefreak.com>,
	Christoph Hellwig <hch@...radead.org>, xfs@....sgi.com,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alex Elder <aelder@....com>
Subject: Re: xfs: very slow after mount, very slow at umount

>>>>> "Mark" == Mark Lord <kernel@...savvy.com> writes:

Mark> On 11-01-27 10:40 AM, Justin Piszcz wrote:
>> 
>> 
>> On Thu, 27 Jan 2011, Mark Lord wrote:
Mark> ..
>>> Can you recommend a good set of mkfs.xfs parameters to suit the characteristics
>>> of this system?  Eg. Only a few thousand active inodes, and nearly all files are
>>> in the 600MB -> 20GB size range.  The usage pattern it must handle is up to
>>> six concurrent streaming writes at the same time as up to three streaming reads,
>>> with no significant delays permitted on the reads.
>>> 
>>> That's the kind of workload that I find XFS handles nicely,
>>> and EXT4 has given me trouble with in the past.
Mark> ..
>> I did a load of benchmarks a long time ago testing every mkfs.xfs option there
>> was, and I found that most of the time (if not all), the defaults were the best.
Mark> ..

Mark> I am concerned with fragmentation on the very special workload
Mark> in this case.  I'd really like the 20GB files, written over a
Mark> 1-2 hour period, to consist of a very few very large extents, as
Mark> much as possible.

Mark> Rather than hundreds or thousands of "tiny" MB sized extents.  I
Mark> wonder what the best mkfs.xfs parameters might be to encourage
Mark> that?

Hmmm, should the application be pre-allocating the disk space then, so
that the writes get into nice large extents automatically?  Isn't this
what the fallocate() system call is for?  Doesn't MythTV use this?

I don't use XFS, or MythTV, but I like keeping track of this stuff.

John
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