Hello All, Kind reminder - no one answered this yet. Did I describe the problem well ? Please let me know if any more information needed. regards --rh ---------- Forwarded message ---------- From: Redwood Hyd <redwoodhyd@xxxxxxxxx> Date: Tue, Dec 17, 2013 at 12:50 PM Subject: raid5 + dm-crypt WRITE perf., higher rrqm/s - kernel 3.10.16 To: linux-raid@xxxxxxxxxxxxxxx Hi All, I am trying to match the WRITE throughput for 512K chunk size to WRITE throughput I am getting with 32K chunk size. My setup is : iozone (4k rec) -> ext4 -> dm-crypt dev mapper + raid5 (4 disks). In my past experience 512K chunk size was not very off from 32K chunk size on kernel 2.6.32 for above situation. >From iostats it seems that 512K is slow because of higher rrqm/s on the physical disks behind raid5 device (last 4 columns are from iostat -x on physical disks behind raid5) Chunk-size iozon MB/s Avgrq-sz r/s rMB/s rrqm/s 512K 25 MBps 976 ~60 ~7.00 ~1800 32K 39 MBps 63 ~20 ~0.55 ~100 Question: Is it that partial stripe happening and causing more reads here ? Question: Can someone suggest some code hacks or config changes such that even with 512K iozone writes to ext4/dm-crypt/raid5 device is close to 39 MBps? Or otherwise more pointers into code to understand and conclude will be helpful Question: Are the changes in dm-crypt or block layer (since 2.6.32) causing higher r/s rMB/s rrqm/s etc. ? How to tune it now? To compare here are same numbers (lower rrqm/s) if I remove dm-crypt : Chunk-size iozon MB/s Avgrq-sz r/s rMB/s rrqm/s 512K 81 MBps 976 ~12 ~0.41 ~100 32K 89 MBps 63 ~01 ~0.04 ~4 Quesiton: Why dm-crypt causing higher r/s rMB/s rrqm/s ( higher these lower write MB/s) ? regards --rh -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
