juoms

Ramdom sequential test launched: slow reads when lun has write-back en

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Hello, I have one problem when a massive random write operation is launched and virtual drive has write-back enabled. Reads are slow while flushing cache.

I was able to reproduce it when I launch two sqlio in parallel:
-one sqlio process writing random (-b8 -o1)

-one sqlio process read random (-b8 -o1)

Drive group: 8xR1 1TB 7.2k, direct io, disk cache disabled. LSI model: 9280 4i4e firmware 12.15.0-0189

Virtual drive with write-back is enabled:
reads
iops/sec: 20, Avg_Latency(ms): 48, Max_Latency(ms): 716
writes
iops/sec: 1346, Avg_Latency(ms): 0, Max_Latency(ms): 0

Virtual drive with write-Throught is enabled:
reads
iops/sec: 142, Avg_Latency(ms): 6, Max_Latency(ms): 26
writes
iops/sec: 106, Avg_Latency(ms): 8, Max_Latency(ms): 35

Is posible slowdown writes having write-back enabled? Writes are fast (wb), but read latency is really high. I tested flush interval (1sg - 60sg) but with no sucess.

Thank youu

Edited by juoms

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