[Linux-cluster] gfs tuning

[Wendy Cheng]

Ross Vandegrift wrote:
> On Mon, Jun 16, 2008 at 11:45:51AM -0500, Terry wrote:
>   
>> I have 4 GFS volumes, each 4 TB.  I am seeing pretty high load
>> averages on the host that is serving these volumes out via NFS.  I
>> notice that gfs_scand, dlm_recv, and dlm_scand are running with high
>> CPU%.  I truly believe the box is I/O bound due to high awaits but
>> trying to dig into root cause.  99% of the activity on these volumes
>> is write.  The number of files is around 15 million per TB.   Given
>> the high number of writes, increasing scand_secs will not help.  Any
>> other optimizations I can do?
>>     
>
>   

A similar case two years ago was solved by the following two tunables:

shell> gfs_tool settune <mount_point> demote_secs <seconds>
(e.g. "gfs_tool settune /mnt/gfs1 demote_secs 200").
shell> gfs_tool settune <mount_point> glock_purge <percentage>
(e.g. "gfs_tool settune /mnt/gfs1 glock_purge 50")

The example above will trim 50% of inode away for every 200 seconds 
interval (default is 300 seconds). Do this on all the GFS-NFS servers 
that show this issues. It can be dynamically turned on (non-zero 
percentage) and off (0 percentage).

As I recalled, the customer used a very aggressive percentage (I think 
it was 100%) but please start from middle ground (50%) to see how it goes.

-- Wendy