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Hi Patrick, OK. It works out that we'll likely need the oss caching mechanism in order to satisfy the new space token requirement (the oss provides a mechanism to use a space token in a meaningful way). So, looks like this one moved up in priority. Andy P.S. I'll take you up on the offer :-) On Mon, 3 Mar 2008, Patrick McGuigan wrote: > Hi Andy, > > I'll let you know how the r/o migration attempt works when I try it later > tonight. > > I think it would be useful to remove the pathname limit under caching, > although I am biased ;) I expect that ATLAS Tier3 sites will take a long > look at Scalla because of the integration with root and the more flexible the > software is, the more likely it will fit the perceived need. I am about to > help setup a Tier3 site where the existing hardware provides three disks per > data server and would be willing to test implementations there. > > Patrick > > Andrew Hanushevsky wrote: >> Hi Patrick, >> >> Yes, you can do what you want to do. The most generc way is to export the >> paths as r/o (read/only). See the xrootd.export directive. You can do what >> you want, though we have never tried it. That is, having a server exporting >> a read/only path that you essentially want to duplicate on a read/write >> server(s). It probably will work. If not, there are a couple of other >> things you can do to force it to work. BTW to keep a single config file, >> simply bracket the exceptional export in an if/fi construct rereferencing >> that host. For instance, >> >> if <problem host> >> xrootd.export /thepath r/o >> else >> xrootd.export /thepath >> fi >> >> I understand your concern about granularity. That problem seems to plague >> many LVMs. The newest ones (i.e., zfs) try to address that issue. So, does >> that mean you think it's worth spending time removing the 255 path limit? >> >> Andy >> >> >> On Mon, 3 Mar 2008, Patrick McGuigan wrote: >> >>> Hi Andy, >>> >>> Is there a way to to enforce a read-only rule for particular data servers? >>> If this is possible, I can ensure that newly written data avoids the >>> systems that need to be "LVM'ed", while allowing the existing data to be >>> read. I am curious if I can replicate data under this scenario using >>> xrdcp, or will I still have to take the read-only systems off-line to move >>> the data? >>> >>> I am concerned about the granularity of recovery actions in our systems >>> under LVM, but I need to support larger pathnames now. The pathnames are >>> being driven by the physics users and the use of metadata in the path >>> components. >>> >>> Patrick >>> >>> Andrew Hanushevsky wrote: >>>> Hi Patrick, >>>> >>>> You are quite right that the design of the cache does impose limits on >>>> file names. The oss was designed almost 10 years ago when there were no >>>> integrated LVM's and few that worked really well and users kept path >>>> names to less that 200 characters. Over the years, as LVM's became >>>> common, the oss turned into the "poor man's LVM". In general, we don't >>>> recommend using it if you have ready access to a suitable LVM. While, >>>> yes, you do give up some features (like fine-grained recoverability and >>>> application-directed partition selection) the other >>>> limitations may be even more annoying. We'll make sure that this >>>> restriction is prominently mentioned in the manual. >>>> >>>> The path you've chosen is about the only one that will work (i.e., >>>> copying off the data and creating a single filesystem using an LVM). >>>> >>>> Now, we do have some ideas on how to remove the pathname length >>>> restriction but wonder if it's really worth the trouble of doing it, >>>> given that LVM's provide practically the same basic features. Any >>>> thoughts? >>>> >>>> Andy >>>> >>>> P.S. What's the driving force for very long path names at your site? >>>> >>>> >>>> On Sat, 1 Mar 2008, Patrick McGuigan wrote: >>>> >>>>> Hi, >>>>> >>>>> Some of our data servers have two disks and I am using the oss.cache >>>>> directive to use both disks to support a single namespace. However, it >>>>> looks like the users of our applications have already run into a >>>>> problem. All of the files are stored in one directory (for a single >>>>> cache) and the filename is the full namespace path with "/" substituted >>>>> with "%". Our problem arises from the fact that full namespace path is >>>>> now limited to the leafname length of the filesystem (255 characters) >>>>> when writing to the cache directory. >>>>> >>>>> I see a couple of ways to mediate the problem; removing one disk or >>>>> using and LVM to create one drive in the OS. I am curious if there are >>>>> other alternatives? >>>>> >>>>> If I have to move to one disk, I would like to migrate the data in the >>>>> existing caches to other data servers while I rework the existing >>>>> system. What is the best way to migrate this data? I am planning on >>>>> taking the "problem" data server off-line and use xrdcp to move the data >>>>> to the other servers. >>>>> >>>>> Regards, >>>>> >>>>> Patrick >>>>> >>> >