Re: GFS2: debugging I/O issues

[Steven Whitehouse <swhiteho@xxxxxxxxxx>]

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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