[Gluster-users] AFR questions

[Keith Freedman]

At 11:00 AM 12/6/2008, Stas Oskin wrote:
>Hi.
>
>did you cat the file through the gluster mount point or on the 
>underlying filesystem.
>the auto-heal is automatically "activated"  but it only "heal's" on 
>file access, so if you access the file through the gluster 
>mountpoint it should find that it's out of date and update from one 
>of the other servers.
>
>check your gluster log. grep for your filename and see what it might 
>say (on both servers)
>
>
>So actually, if the server goes down, the file will not be 
>replicated until it's accessed?
>
>AFAIK it's not a very good approach, because it means that you need 
>somehow re-access all the files on the lost server in order to 
>replicated them. Otherwise, the single copy of the file could be 
>entirely lost, when the other server with it goes down as well.

this has been glusters approach from the beginning..  if you read the 
wiki, there are recommendations for how to force auto-healing.  look 
for some find commands what will do what you want.

While, form a raw high-availability approach, the on-access healing 
doesn't really help when faced with potential of multiple failures, 
from a performance approach it's ideal.
otherwise, each AFR server has to retain a transaction log.  This 
would likely have to be stuck on the underlying filesystem, as some 
weird file or something, or just consume vast amounts of memory.

so while it may not be ideal in your circumstance, knowing how it 
behaves and knowing how to force auto-healing should make it work well for you.

>Any idea?