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* Continually increasing inflight IO statistics with md mirror and blk-mq enabled on 3.19 release
@ 2015-02-26 2:22 james owens
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From: james owens @ 2015-02-26 2:22 UTC (permalink / raw)
Please cc me personally on any replies as I am not a subscriber to the
I currently have a 2 device md raid 1 on my Linux workstation where the
slave devices are usb 3.0 external drives 4 TB each which I use for
backup purposes. I also have a 3ware 9750 RAID controller with a HW RAID
1 SSD mirror and 12 drive RAID 6.
I recently installed the 3.19 release kernel from openSuSE current to
try out the block-mq optimizations. The new mq subsystem is clearly
enabled by the presence of the mq subdirectory under /sys/block/foo. The
performance on the 3ware is great, especially the SSD mirror; however,
when using the md RAID 1 with external USB 3.0 devices, I noticed the
inflight IO counters at /sys/block/md127/inflight are continuously
increasing. This is not normal as these should go to 0 once any pending
reads/writes are finalized. Is this simply an accounting problem I can
safely ignore, or is it an unsafe situation that I need to be concerned
Note that this does not occur with the exported disks on the 3ware array
/dev/sda and /dev/sdb.
I could try and see if this happens with a plain USB drive as I have
If you dismount the volume and stop the md array and then reassemble it,
the statistics reset (as one would expect).
I use a bitmap file to speed up resyncs, and the bitmap file is
clearing, and there is no filesystem corruption that I can see, so the
writes are clearly getting to the disks correctly.
I will provide more information as best I can if needed. My guess is
that this will be pretty easy to reproduce.
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2015-02-26 2:22 Continually increasing inflight IO statistics with md mirror and blk-mq enabled on 3.19 release james owens
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