[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: [dm-devel] Substantial performance difference when reading/writing to device-mapper vs. the individual device



Reply to self:

Could it be explained by the difference in max_segments between the different devices and the dm device?
Sounds like https://bugzilla.redhat.com/show_bug.cgi?id=755046 which is supposed to be fixed in 6.4, I reckon:

 

3514f0c5615a00003 dm-3 XtremIO,XtremApp

size=1.0T features='0' hwhandler='0' wp=rw

`-+- policy='queue-length 0' prio=1 status=active

  |- 0:0:2:2 sdi  8:128  active ready running

  |- 0:0:3:2 sdl  8:176  active ready running

  |- 0:0:1:2 sdf  8:80   active ready running

  |- 0:0:0:2 sdc  8:32   active ready running

  |- 1:0:0:2 sds  65:32  active ready running

  |- 1:0:3:2 sdab 65:176 active ready running

  |- 1:0:2:2 sdy  65:128 active ready running

  `- 1:0:1:2 sdv  65:80  active ready running

 

[root lg545 ~]# cat /sys/class/block/dm-3/queue/max_segments

128

[root lg545 ~]# cat /sys/class/block/sdi/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdl/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdf/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdc/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sds/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdab/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdy/queue/max_segments

1024

[root lg545 ~]# cat /sys/class/block/sdv/queue/max_segments

1024



On Mon, Jul 22, 2013 at 2:47 PM, Kaul <mykaul gmail com> wrote:
We are seeing a substantial difference in performance when we perform a read/write to /dev/mapper/... vs. the specific device (/dev/sdXX)
What can we do to further isolate the issue?

We are using CentOS 6.4, with all updates, 2 CPUs, 4 FC ports:
Here's a table comparing the results:

# of LUNs

# of Paths per device

Native Multipath Device

IO Pattern

IOPS

Latency Micro

BW KBps

4

16

No

100% Read

605,661.4

3,381

2,420,736

4

16

No

100% Write

477,515.1

4,288

1,908,736

8

16

No

100% Read

663,339.4

6,174

2,650,112

8

16

No

100% Write

536,936.9

7,628

2,146,304

4

16

Yes

100% Read

456,108.9

1,122

1,824,256

4

16

Yes

100% Write

371,665.8

1,377

1,486,336

8

16

Yes

100% Read

519,450.2

1,971

2,077,696

8

16

Yes

100% Write

448,840.4

2,281

1,795,072



[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]