Messages in this thread | | | Date | Wed, 25 Feb 2015 21:22:34 -0500 (EST) | From | james owens <> | Subject | Continually increasing inflight IO statistics with md mirror and blk-mq enabled on 3.19 release |
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Please cc me personally on any replies as I am not a subscriber to the list.
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 about?
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 some available.
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.
Best regards,
Jim Owens
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