There's a recent ticket discussing the behavior of ceph-fuse after the machine it's running on has been suspended: http://tracker.ceph.com/issues/8291 In short, CephFS clients which are disconnected from the cluster for a sufficiently long time are generally forbidden from reconnecting — after a configurable timeout, their "capabilities" on inodes and dentries are revoked, and other users are allowed to change them. If the client then comes back, it's entirely possible it has incompatible changes to the tree, so we don't let it reconnect in order to prevent that. (We could make the system smarter in some situations, if for instance nobody has changed the given filesystem data in the meanwhile, but that's hard and a problem for another day.) Apparently, ceph-fuse does exactly this, as we expect (although we have newly-merged features which let the admin force a reconnect). But the kernel client does allow a reconnect. I haven't done this myself, so the first question is just a fact check for Sage or Zheng: 1) What is the kernel client doing after suspend? Does it in fact reconnect under situations where ceph-fuse won't, and what are they? More interestingly, while suspended systems aren't part of our normal target use case, they'd be nice to support well. The trivial solution would be to somehow flush out all dirty data on suspend, and then on wake or when we discover we have a reset session, we can clean out our cache and reconnect as a new client if we have no dirty data. Unfortunately, I don't know anything about Linux's suspend functionality or APIs, and my weak attempts at googling and grepping aren't turning anything up. So a question to everybody: 2) What notifications does Linux send, and what filesystem mechanisms does it invoke, when it is suspending? I see that it has in the past forced a sync whenever suspending, but I think that's no longer required. Are there other interfaces we can rely on, or use heuristically? -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
