Ronald Kuehn writes: > On Sunday, August 26, 2007 at 16:36:26 CEST, Rainer J.H. Brandt wrote: > > > Ronald Kuehn writes: > > > No. You can neither access ZFS nor UFS in that way. Only one > > > host can mount the file system at the same time (read/write or > > > read-only doesn't matter here). > > > > I can see why you wouldn't recommend trying this with UFS > > (only one host knows which data has been committed to the disk), > > but is it really impossible? > > > > I don't see why multiple UFS mounts wouldn't work, if only one > > of them has write access. Can you elaborate? > > Hi, > > UFS wasn't designed as a shared file system. The kernel > always assumes it is the only party accessing or modifying > any on-disk data structures. With that premise it uses caching > quite heavily. The view of the file system (cached structures + on-disk > state) is consistent. The on-disk state alone isn't while the > file system is mounted. Any other system accessing the on-disk > state w/o taking into consideration the data cached on the original > host will probably see inconsistencies. This will lead to data corruption > and panics. If only one system mounts the file system read/write > and other hosts only mount it read-only the read-only hosts will > get an inconsistent view of the file system because they don't know > what's in the cache of the r/w host. > > These approaches exist to solve this problem: > - Only allow one host to directly access the file system. Other > systems access it by talking over the network to this host: > + NFS > + the pxfs layer of Sun Cluster (global file system) > - Use a file system designed with some kind of co-ordination for parallel > access to the on-disk data structures built in: > + QFS (Shared mode uses a meta data server on one host to > manage the right to access certain parts of the on-disk structures. > The operation on the data itself then takes place over the storage > path. In that case multiple systems can modify on-disk structures > directly. They only need to ask the meta data server for permission.) > > I hope that helps, > Ronald
Yes, thank you for confirming what I said. So it is possible, but not recommended, because I must take care not to read from files for which buffers haven't been flushed yet. Rainer Brandt _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
