[ale] Performance issue

Ted W. ted-lists at xy0.org
Sat Aug 20 18:49:43 EDT 2016


If you didn't already, try either iostat as `iostat -xm 1` or `sar -d`.
You see any unusual await or anything else that sticks out?

What FS? LVM?

A shot in the dark might lead me to check the FS alignment with fdisk but that
seems like an awfully large performance hit for something like that.

-Ted

On Fri, Aug 19, 2016 at 10:26:22AM -0400, Jim Kinney wrote:
>    Getting DISMAL performance from new hardware.
> 
>    Twin 6-core Xeon E5-2630L v.2 @2.40 GHz
>    128GB DDR4 RAM
>    LSI megaraid 2108 in a PCIe v3 slot
>    Onboard LSI 3108
>    Drives are all 6Gbps SAS2 4TB
>    2 arrays, RAID 6, one is 40Tb, other 104TB
> 
>    Everything hardware says I should expect a minimum through put of
>    12Gbps on either array.
> 
>    The max I'm getting from iotop is 784 Mbps.
> 
>    W. T. F!!!
> 
>    According to top, the system is basically idle. Ditto from iostat and
>    every other tool I check. I'm doing a 'cp -a' from/to same array.
> 
>    Yes. New location is Luks encrypted. That process is totally asleep
>    it's getting so little work. The rng is busy (dev/random is not running
>    out (watch -n 1 cat /proc/sys/kernel/random/entropy_avail was always
>    above 2048)) but not overloaded or asleep.
> 
>    Tested going unencrypted to unencrypted with similar performance.
> 
>    Changed tuned-adm to latency-performance from balanced and the read
>    portion of the cp went to 0 bps for 20 seconds until I switched it back
>    to balanced mode. So that was a fail. It improved greatly using
>    throughout-performance mode (bursts of 250MB/s) but was still showing
>    long periods of 0 writes. Load went up from a paltry 8 to 22 so it's
>    working more.
> 
>    But top shows wa values across multiple cores hitting 100 so it's
>    hitting a wall somewhere.
> 
>    Any ideas of more places to look?

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