[ale] Performance issue

[DJ-Pfulio]

Bus specifications have little to do with spinning disk performance, as
you know.

What is the max for each drive to read?  120-180Mbps?  How are the
arrays striped?  4-way, 8-way?  That would mean at 4 x 120Mbps (480Mbps)
is the highest possible throughput I'd expect. 960Mbps if 8-way stripe
... there is overhead ... so 800Mbps seems reasonable to me.

http://wintelguy.com/raidperf.pl is more pessimistic on performance. I'm
not convinced this numbers are MB/s. Think they are Mb/s.

On 08/20/2016 06:49 PM, Ted W. wrote:
> 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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