[gpfsug-discuss] AFM limitations in a multi-cluster environment, slow prefetch operations

[Sven Oehme]

Hi Bryan,

in 4.1 AFM uses multiple threads for reading data, this was different in
3.5 . what version are you using ?

thx. Sven


On Mon, Oct 6, 2014 at 8:36 AM, Bryan Banister <bbanister at jumptrading.com>
wrote:

>  Just an FYI to the GPFS user community,
>
>
>
> We have been testing out GPFS AFM file systems in our required process of
> file data migration between two GPFS file systems.  The two GPFS file
> systems are managed in two separate GPFS clusters.  We have a third GPFS
> cluster for compute systems.  We created new independent AFM filesets in
> the new GPFS file system that are linked to directories in the old file
> system.  Unfortunately access to the AFM filesets from the compute cluster
> completely hang.  Access to the other parts of the second file system is
> fine.  This limitation/issue is not documented in the Advanced Admin Guide.
>
>
>
> Further, we performed prefetch operations using a file mmafmctl command,
> but the process appears to be single threaded and the operation was
> extremely slow as a result.  According to the Advanced Admin Guide, it is
> not possible to run multiple prefetch jobs on the same fileset:
>
> GPFS can prefetch the data using the *mmafmctl **Device **prefetch –j **FilesetName
> *command (which specifies
>
> a list of files to prefetch). Note the following about prefetching:
>
> v It can be run in parallel on multiple filesets (although more than one
> prefetching job cannot be run in
>
> parallel on a single fileset).
>
>
>
> We were able to quickly create the “--home-inode-file” from the old file
> system using the mmapplypolicy command as the documentation describes.
> However the AFM prefetch operation is so slow that we are better off
> running parallel rsync operations between the file systems versus using the
> GPFS AFM prefetch operation.
>
>
>
> Cheers,
>
> -Bryan
>
>
>
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