Hi All, Here is a breief writeup on AFR: AFR volume is specified as volume afr-example type cluster/afr subvolumes client1 client2 client3 client4 option replicate *pdf:4,*txt:3,*png:2,*:1 option self-heal on # by default this is on option debug off # by default this is off, should be turned on only during debugging as it produces huge logs end-volume As it can be inferred from "option replicate", pdf files will be replicated across all 4 children, text files across first 3 children (client1 client2 client3), png files across first 2 children (client1 client2) and rest of the files are put on 1st child i.e client1. Note that AFR does not schedule the creation of files in the case where number of replica 'n' is less than the number of children., it will just create it among the first 'n' children. Self-heal feature has been introduced in 1.3.0 pre5 release. Selfheal tracks the file updation using external attributes on the files. Hence xattr support is needed by the backend filesystem. Most filesystems (ext3 xfs reiserfs) support extended attributes. You can check if your filesystem supports (or enabled) xattr by following commands in the backend: you can set an xattr like this: setfattr -n user.test -v 123 file.c you can get it like this: getfattr -n user.test file.c Each file will have two xattrs: trusted.afr.createtime - time when the file was created (number of seconds since epoch) trusted.afr.version - number of times a file was edited. (version will be 1 when its created) If we consider above volume specification, in case of txt files, it should have 3 copies. When open() is called on a file say test.txt, it makes sure that all the 3 copies are present on the first 3 children, if not, it will pick the latest version and update it on the children whereever it needs to be updated by checking the createtime and version. * during selfheal, the file with latest createtime with latest version is considered as the latest version. * missing files will not be created in more than first 3 children (*txt:3) * In case a file was found in 4th child too and if it was outdated, it will be updated too (this can happen when 1st child was down and the file was created - during which it will be created on 2nd 3rd 4th children) Missing directories are detected and created in lookup calls. A lookup call is used by kernel/fuse to find the inode number of directory/file.
