Re: How to flush the writing cache before a test with read

[Steven Pratt <slpratt@austin.ibm.com>]

Dan Le wrote:
> Greetings,
>
> FIO needs to write data files in order to read them. Without disabling
> the write-cache of the disk, I was wondering if there's a way to flush
> these data cache to disk right before FIO starts to read these files.
>   
Fio does an fsync and an FADVISE_DONT_NEED call after file creation 
phase which causes the cache to be dropped. I have never had a problem 
with files still being in cache when a read test starts.  The only one 
to watch out for is if you repeat the test, the files may be in cache 
from a previous read, as the default behavior is to not delete on 
completion and to not re-create if they already exist.

Steve

> I don't want to run every second "sync && echo 3 >
> /proc/sys/vm/drop_caches" at the same time with FIO because of its
> incurred overhead. Please help.
>
> Thank you,
>
> Dan
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