Hi,
We benchmarked the md raid driver performance on 3-18-rc3 kernel and
compared the results with that of 3.6.11. The reason for this exercise
is to understand if multithreaded raid driver has any performance
benefits over 3.6.11 which is single threaded. Here are some details
about the setup
System: Intel(R) Xeon(R) CPU E3-1230 V2 @ 3.30GHz 4 cores (8threads),
8GB RAM.
Setup: 3 SSDs create a raid5 array
test tool: iozone (only read/re-read, write/re-write tested), blocksize:
4k-64k, filesize: 1Gig to 200Gig
Comparison was done for speed of data transfer in kBytes/sec and also
the CPU utilization as reported by iozone.
raid on 3.18.0-rc3 performed much worse than raid on 3.6.11.
Read/Write: raid on 3.18.0-rc3 operated at almost half the speed of raid
on 3.6.11
CPU Utilization: With md raid on 3.18.0-rc3, the CPU utilization was
less than half of md raid on 3.6.11 on WRITE operations. However, for
READ operations, 3.18-0.rc3 had more CPU utilization than 3.6.11.
Also, I noticed that scaling up the CPU cores of the system scales down
the raid througput with 3.18.0-rc3.
I do have detailed logs of the comparison but I'm not sure I should send
those on this mailing list.
If my observation aligns with someone else's, then what is really the
gain with multithreaded raid.
Manish
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