Gfid-access Translator

The 'gfid-access' translator provides access to data in glusterfs using a virtual path. This particular translator is designed to provide direct access to files in glusterfs using its gfid. 'GFID' is glusterfs's inode number for a file to identify it uniquely. As of now, Geo-replication is the only consumer of this translator. The changelog translator logs the 'gfid' with corresponding file operation in journals which are consumed by Geo-Replication to replicate the files using gfid-access translator very efficiently.

Implications and Usage

A new virtual directory called '.gfid' is exposed in the aux-gfid mount point when gluster volume is mounted with 'aux-gfid-mount' option. All the gfids of files are exposed in one level under the '.gfid' directory. No matter at what level the file resides, it is accessed using its gfid under this virutal directory as shown in example below. All access protocols work seemlessly, as the complexities are handled internally.

Testing

1. Mount glusterfs client with '-o aux-gfid-mount' as follows.

   mount -t glusterfs -o aux-gfid-mount :

   Example:

   #mount -t glusterfs -o aux-gfid-mount rhs1:master /master-aux-mnt
   

2. Get the 'gfid' of a file using normal mount or aux-gfid-mount and do some operations as follows.

   getfattr -n glusterfs.gfid.string

   Example:

   #getfattr -n glusterfs.gfid.string  /master-aux-mnt/file
   # file: file
   glusterfs.gfid.string="796d3170-0910-4853-9ff3-3ee6b1132080"
   
   #cat /master-aux-mnt/file
   sample data
   
   #stat /master-aux-mnt/file
      File: `file'
      Size: 12             Blocks: 1          IO Block: 131072 regular file
    Device: 13h/19d        Inode: 11525625031905452160  Links: 1
    Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/   root)
    Access: 2014-05-23 20:43:33.239999863 +0530
    Modify: 2014-05-23 17:36:48.224999989 +0530
    Change: 2014-05-23 20:44:10.081999938 +0530
   

3. Access files using virtual path as follows.

   /mountpoint/.gfid/<actual-canonical-gfid-of-the-file>'

   Example:

   #cat /master-aux-mnt/.gfid/796d3170-0910-4853-9ff3-3ee6b1132080
   sample data
   #stat /master-aux-mnt/.gfid/796d3170-0910-4853-9ff3-3ee6b1132080
      File: `.gfid/796d3170-0910-4853-9ff3-3ee6b1132080'
      Size: 12             Blocks: 1          IO Block: 131072 regular file
    Device: 13h/19d        Inode: 11525625031905452160  Links: 1
    Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/   root)
    Access: 2014-05-23 20:43:33.239999863 +0530
    Modify: 2014-05-23 17:36:48.224999989 +0530
    Change: 2014-05-23 20:44:10.081999938 +0530
   

We can notice that 'cat' command on the 'file' using path and using virtual path displays the same data. Similarly 'stat' command on the 'file' and using virtual path with gfid gives same Inode Number confirming that its same file.

Nature of changes

This feature is introduced with 'gfid-access' translator.