On 01/30/2015 06:28 PM, Jeff Darcy wrote:
Pranith and I had a discussion regarding this issue and here is what we have
in our mind right now.
We plan to provide the user commands to execute from mount so that he can
access the files in split-brain. This way he can choose which copy is to be
used as source. The user will have to perform a set of getfattrs and
setfattrs (on virtual xattrs) to decide which child to choose as source and
inform AFR with his decision.
A) To know the split-brain status :
getfattr -n trusted.afr.split-brain-status <path-to-file>
This will provide user with the following details -
1) Whether the file is in metadata split-brain
2) Whether the file is in data split-brain
It will also list the name of afr-children to choose from. Something like :
Option0: client-0
Option1: client-1
We also tell the user what the user could do to view metadata/data info; like
stat to get metadata etc.
B) Now the user has to choose one of the options (client-x/client-y..) to
inspect the files.
e.g., setfattr -n trusted.afr.split-brain-choice -v client-0 <path-to-file>
We save the read-child info in inode-ctx in order to provide the user access
to the file in split-brain from that child. Once the user inspects the file,
he proceeds to do the same from the other child of replica pair and makes an
informed decision.
C) Once the above steps are done, AFR is to be informed with the final choice
for source. This is achieved by -
(say the fresh copy is in client-0)
e.g., setfattr -n trusted.afr.split-brain-heal-finalize -v client-0
<path-to-file>
This child will be chosen as source and split-brain resolution will be done.
+1
That looks quite nice, and AFAICT shouldn't be prohibitively hard to
implement.
The only problem I see is kernel read caching which may come in the way.
We may have to invoke fuse_invalidate if it comes in the way. We will
find out once we implement this.
Pranith
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