Re: speedup ceph / scaling / find the bottleneck

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Another BIG hint.

While doing random 4k I/O from one VM i archieve 14k I/Os. This is 
around 54MB/s. But EACH ceph-osd machine is writing between 500MB/s and 
750MB/s. What do they write?!?!

Just an idea?:
Do they completely rewrite EACH 4MB block for each 4k write?

Stefan

Am 29.06.2012 15:02, schrieb Stefan Priebe - Profihost AG:
> Am 29.06.2012 13:49, schrieb Mark Nelson:
>> I'll try to replicate your findings in house.  I've got some other
>> things I have to do today, but hopefully I can take a look next week. If
>> I recall correctly, in the other thread you said that sequential writes
>> are using much less CPU time on your systems?
>
> Random 4k writes: 10% idle
> Seq 4k writes: !! 99,7% !! idle
> Seq 4M writes: 90% idle
>
>
>  >  Do you see better scaling in that case?
>
> 3 osd nodes:
> 1 VM:
> Rand 4k writes: 7000 iops
> Seq 4k writes: 19900 iops
>
> 2 VMs:
> Rand 4k writes: 6000 iops each
> Seq 4k writes: 4000 iops each VM 1
> Seq 4k writes: 18500 iops each VM 2
>
>
> 4 osd nodes:
> 1 VM:
> Rand 4k writes: 14400 iops
> Seq 4k writes: 19000 iops
>
> 2 VMs:
> Rand 4k writes: 7000 iops each
> Seq 4k writes: 18000 iops each
>
>
>
>> To figure out where CPU is being used, you could try various options:
>> oprofile, perf, valgrind, strace.  Each has it's own advantages.
>>
>> Here's how you can create a simple callgraph with perf:
>>
>> http://lwn.net/Articles/340010/
> 10s perf data output while doing random 4k writes:
> https://raw.github.com/gist/2c16136faebec381ae35/09e6de68a5461a198430a9ec19dfd5392f276706/gistfile1.txt
>
>
> Stefan