linux-kernel - Re: rm -f * on large files very slow on XFS + MD RAID 6 volume of 15x 4TB of HDDs (52TB)

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Message-ID: <20140423021835.GI15995@dastard>
Date:	Wed, 23 Apr 2014 12:18:35 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Speedy Milan <speedy.milan@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ivan Pantovic <gyro.ivan@...il.com>,
	xfs@....sgi.com
Subject: Re: rm -f * on large files very slow on XFS + MD RAID 6 volume of
 15x 4TB of HDDs (52TB)

[cc xfs@....sgi.com]

On Mon, Apr 21, 2014 at 10:58:53PM +0200, Speedy Milan wrote:
> I want to report very slow deletion of 24 50GB files (in total 12 TB),
> all present in the same folder.

total = 1.2TB?

> OS is CentOS 6.4, with upgraded kernel 3.13.1.
> 
> The hardware is a Supermicro server with 15x 4TB WD Se drives in MD
> RAID 6, totalling 52TB of free space.
> 
> XFS is formated directly on the RAID volume, without LVM layers.
> 
> Deletion was done with rm -f * command, and it took upwards of 1 hour
> to delete the files.
> 
> File system was filled completely prior to deletion.

Oh, that's bad. it's likely you fragmented the files into
millions of extents?

> rm was mostly waiting (D state), probably for kworker threads, and

No, waiting for IO.

> iostat was showing big HDD utilization numbers and very low throughput
> so it looked like a random HDD workload was in effect.

Yup, smells like file fragmentation. Non-fragmented 50GB files
should be removed in a few milliseconds. but if you've badly
fragmented the files, there could be 10 million extents in a 50GB
file. A few milliseconds per extent removal gives you....

Cheers,

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