Filesize * nrfiles is no equal to actual I/O size when the filesize option is set too small and size option is not specified

[KeisukeeLee]

Please acknowledge the following before creating a ticket

• I have read the GitHub issues section of REPORTING-BUGS.

Description of the bug:

I use fio as follow command(specify filesize and nrfiles option, but no specify size option): fio --name=read --ioengine=sync --rw=read --bs=4k --numjobs=1 --filesize=30K --nrfiles=1 --end_fsync=1 - -direct=1, I find out that the total aggregate io is only 28.0KiB, but filesize * nrfiles=30K*1=30K, I thought that the two should be equal.

When I tryfio --name=read --ioengine=sync --rw=read --bs=4k --numjobs=1 --filesize=30Mi --nrfiles=1 --end_fsync=1 --direct=1(I change --filesize to 30Mi), the result is as expected.

So, what happens when it read small sized file?
Environment:
WSL2(Ubuntu) in Windows10
fio version:
Version: 3.16-1
Reproduction steps

fio --name=read --ioengine=sync --rw=read --bs=4k --numjobs=1 --filesize=30K --nrfiles=1 --end_fsync=1 - -direct=1andfio --name=read --ioengine=sync --rw=read --bs=4k --numjobs=1 --filesize=30Mi --nrfiles=1 --end_fsync=1 --direct=1

[vincentkfu]

Fio can't write 30k because your block size is 4k.

[KeisukeeLee]

Thx! @vincentkfu

[KeisukeeLee]

Also, When I run the following command, fio --name=read --ioengine=sync --rw=read --bs=4k --numjobs=1 --filesize=1Ki-50Ki --nrfiles=1000 --end_fsync=1, there's always a file that doesn't get created, it finally spits out an error: fio: pid=349, err=2/file:filesetup.c:701, func=open(read.0.7), error=No such file or directory. Is that the same thing? If so, I think it's a bit weird.