[Linux-cluster] GFS2: debugging I/O issues

[Steven Whitehouse]

Hi,

On 08/04/16 10:21, Daniel Dehennin wrote:
> Hello,
>
> On our virtualisation infrastructure we have a 4To GFS2 over a SAN.
>
> Since one or two weeks we are facing read I/O issues, 5k or 6k IOPS with
> an average block size of 5kB.
>
> I'm looking for the possibilities and didn't find anything yet, so my
> question:
>
>      Is it possible that reaching over 80% use of the GFS2 can produce
>      such workload?
>
> Regards.
>
>
>

If you are worried about read I/O, then I'd look carefully at the 
fragmentation using filefrag on a few representative files to see how 
they are laid out on disk. There are other possible causes of 
performance issues too - do you have the fs mounted noatime (which we 
recommend for most use cases) for example?

Running a filesystem which is close to the capacity limit can generate 
fragmentation over time, 80% would usually be ok, and more recent 
versions of GFS2 are better than older ones at avoiding fragmentation in 
such circumstances,

Steve.

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