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Hi Gregory, The answers are based on the assumption that you will be using the libXrdOfs.so filesystem implementation. > 1. When a request is made for a file that has to be staged from an HSM > server, we would like to get back either: > a) an estimate of how long it will be before the file is ready for > reading, or The wait message that comes back when you open a file that has to be staged should have the estimated time (including the fact that the file is being staged). However, I found that the time is notriously unreliable because small delays in file staging can produce erractic global effects, One of those "butterfly in the canyon" type of things. > b) a least a bit indicating that this request will wait for staging. > Is this possible without "major" changes? The "prepare" request looks > like it has space for an arbitrary response, but it isn't clear to me > from the protocol description how arbitrary it really is. It may be > that open needs to send back an indicator as well, but that may be > harder. Prepare is not conducive to time estimates because the estimates canot be dertermined. A request may be scattered across multiple servers and at that point it's impossible to calculate what will happen. Anyway, prepare is a best-effort scheme. If prepare doesn't work or is tossed (which it can be), the actual open will cause the file to fault in. > 2. Is there a way to pin a file once it has been staged to a disk > server, so that it is not a candidate for removal from the server? If > so, is this done on a per-file basis, and/or a per-directory basis? In the mps reference (assuming your will be using mps), describes how to use "pin files" to "pin" a file in the disk cache for various reasons (e.g., don't unpin until after first use, pin until a certain date, or pin for so much time). > 3. Is there anyway a file can be dropped from a disk server while a > client has it "open"? If so, will subsequent access attempts result in > a new redirect or recache attempt? You can always erase a file. If the file is open, current users will continue to use the file while new users will have the file staged (elsewhere or perhaps even the same machine). In general, if a file is lost while it is being used, the system will attempt to either find another copy or restage it if none can be found. > 4. Does xrootd automatically replicate a file to an additional server > if demand for that file gets too high for a single server to sustain? > All that I've read suggests that it does, but I'm having a little > trouble tracking down the code that does the work. Yes. There is no explicit code. It's just the way it works. Once a server becomes overloaded (assuming you've defined what it means for a server to be overloaded), the redirector will redirect clients to a less loaded server causing a file replication (that assumes the file is stageable). Andy