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....