[gpfsug-discuss] Migration to separate metadata and data disks

[Aaron Knister]

I must admit, I'm curious as to the reason you're dropping the 
replication factor from 2 down to 1. There are some serious advantages 
we've seen to having multiple metadata replicas, as far as error 
recovery is concerned.

Could you paste an output of mmlsdisk for the filesystem?

-Aaron

On 9/1/16 9:30 AM, Miroslav Bauer wrote:
> Hello,
>
> I have a GPFS 3.5 filesystem (fs1) and I'm trying to migrate the
> filesystem metadata from state:
> -m = 2 (default metadata replicas)
> - SATA disks (dataAndMetadata, failGroup=1)
> - SSDs (metadataOnly, failGroup=3)
> to the desired state:
> -m = 1
> - SATA disks (dataOnly, failGroup=1)
> - SSDs (metadataOnly, failGroup=3)
>
> I have done the following steps in the following order:
> 1) change SATA disks to dataOnly (stanza file modifies the 'usage'
> attribute only):
> # mmchdisk fs1 change -F dataOnly_disks.stanza
> Attention: Disk parameters were changed.
>   Use the mmrestripefs command with the -r option to relocate data and
> metadata.
> Verifying file system configuration information ...
> mmchdisk: Propagating the cluster configuration data to all
>   affected nodes.  This is an asynchronous process.
>
> 2) change default metadata replicas number 2->1
> # mmchfs fs1 -m 1
>
> 3) run mmrestripefs as suggested by output of 1)
> # mmrestripefs fs1 -r
> Scanning file system metadata, phase 1 ...
> Error processing inodes.
> No space left on device
> mmrestripefs: Command failed.  Examine previous error messages to
> determine cause.
>
> It is, however, still possible to create new files on the filesystem.
> When I return one of the SATA disks as a dataAndMetadata disk, the
> mmrestripefs
> command stops complaining about No space left on device. Both df and mmdf
> say that there is enough space both for data (SATA) and metadata (SSDs).
> Does anyone have an idea why is it complaining?
>
> Thanks,
>
> --
> Miroslav Bauer
>
>
>
>
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-- 
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776