Hi all,

When using fio configuration below..

[global]
ioengine=libaio
direct=1
runtime=600
bs=32k
iodepth=8
rw=randrw
rwmixread=80
percentage_random=100,0

[drive1]
filename=/dev/sda


I am expecting to see 80% reads, 20% writes where all reads are random and all 
writes are sequential. I captured a bus trace of traffic to the disk and the 
bus trace reflected as much with one issue. The write commands are essentially 
random. Each write begins at a new random LBA. If 2 or more writes occur in a 
row, the LBA's are sequential based on the block size BUT I feel the heart of 
this feature would be to emulate a large file write during random access. With 
that in mind would it be possible for sequential reads or writes within mixed 
sequential/random workload to remember the last LBA accessed? In this scenario 
the writes would still only take up 20% of the workload but when a write did 
occur it should be the next sequential step from the last write.


Snippet from the bus trace for reference

Command                                           LBA
Read FPDMA Queued:                  19F3F818
Read FPDMA Queued:                  1CBE2740
Write FPDMA Queued:                 24E35198
Write FPDMA Queued:                 24E351A0
Read FPDMA Queued:                  115A9E10
Write FPDMA Queued:                 A3C1968
Read FPDMA Queued:                  20B89488
Write FPDMA Queued:                 336EE0D0
Write FPDMA Queued:                 336EE0D8



Let me know what you think, this feature may be working as intended but it 
seemed off to me.

Thanks,
Stephen "Nick" Nichols
Western Digital
Enterprise Test Development

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