(Illustration by Gaich Muramatsu)
There is a bit more to replication than is said here. AFS and DCE/DFS have "replication" which is merely like a "cron" job. Every so often the read only replicas are updated. Coda has true real time replication servers, and additionally high availability by allowing updates in partitioned groups of servers. If diverging replicaas arise due to server or network outages, then Coda's resolution mechanism will generally fix them up (unless they are true conflicts). The basic mechanism here is as follows: - client gets version stamp from all servers carrying an object - if these agree, file or directory is read from a randomly chosen server - if these differ, client instructs the server to resolve differences. Coda needs very extensive versioning information to do this, which is not present in AFS or DCE/DFS metadata - one needs to be able to detect that certain servers have missed updates, i.e. there is a partial ordering on the versions of files, which is implemented with version vectors. It is also my impression that the Windows 2000 and NT directory replication are more like that of AFS, and not like Coda. There is a similar issue going on in reintegration after disconnected operation. This can be done with AFS as both Transarc and ARLA have demonstrated. But AFS lacks versioning information which allows Coda to easily resume after a failed reintegration - unlike the server replication where AFS is really lacking meta data, this one isn't too serious probably. - Peter - On Sat, 5 Jun 1999, _Oliver,.Thuns: wrote: > >It also supports replicated servers, which are > >aimed at providing higher availability to clients. > > You could also replicate servers with AFS, but only read-only (and one > read-write). Could coda provide replicated servers with write access? yes, u could. coda assumes that write-write conflicts are rare(mostly true) and proceeds, in case there are conflicts u will have to manually resolve the confilcts. HTH -regards radha krishnaReceived on 1999-06-05 14:43:46