On Tue, 28 Aug 2007, Charles DeBardeleben wrote: > Are you sure that UFS writes a-time on read-only filesystems? I do not think > that it is supposed to. If it does, I think that this is a bug. I have > mounted > read-only media before, and not gotten any write errors. > > -Charles
I think what might've been _meant_ here is sharing a UFS filesystem via NFS to different clients, some or all of which mount that 'NFS export' readonly. On the NFS server, you'll still see write activity on the backing filesystem - for access time updates. That's in the context of this thread - "shared filesystem". UFS if mounted readonly should not write to the medium. Definitely not for atime updates. FrankH. > > David Olsen wrote: >>> On 27/08/2007, at 12:36 AM, Rainer J.H. Brandt wrote: >>> >>>> Sorry, this is a bit off-topic, but anyway: >>>> >>>> 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? >>>> >>> Even with a single writer you would need to be >>> concerned with read >>> cache invalidation on the read-only hosts and >>> (probably harder) >>> ensuring that read hosts don't rely on half-written >>> updates (since >>> UFS doesn't do atomic on-disk updates). >>> >>> Even without explicit caching on the read-only hosts >>> there is some >>> "implicit caching" when, for example, a read host >>> reads a directory >>> entry and then uses that information to access a >>> file. The file may >>> have been unlinked in the meantime. This means that >>> you need atomic >>> reads, as well as writes. >>> >>> Boyd >>> _______________________________________________ >>> zfs-discuss mailing list >>> zfs-discuss@opensolaris.org >>> http://mail.opensolaris.org/mailman/listinfo/zfs-discu >>> ss >>> >> >> It's worse than this. Consider the read-only clients. When you access a >> filesystem object (file, directory, etc.), UFS will write metadata to update >> atime. I believe that there is a noatime option to mount, but I am unsure >> as to whether this is sufficient. >> >> my 2c. >> --Dave >> >> >> This message posted from opensolaris.org >> _______________________________________________ >> zfs-discuss mailing list >> zfs-discuss@opensolaris.org >> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >> > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
