On Thu, Feb 19, 2009 at 09:59:01AM -0800, Richard Elling wrote: > Gary Mills wrote: > >Should I file an RFE for this addition to ZFS? The concept would be > >to run ZFS on a file server, exporting storage to an application > >server where ZFS also runs on top of that storage. All storage > >management would take place on the file server, where the physical > >disks reside. The application server would still perform end-to-end > >error checking but would notify the file server when it detected an > >error. > > Currently, this is done as a retry. But retries can suffer from cached > badness.
So, ZFS on the application server would retry the read from the storage server. This would be the same as it does from a physical disk, I presume. However, if the checksum failure persisted, it would declare an error. That's where the RFE comes in, because it would then notify the file server to utilize its redundant data source. Perhaps this could be done as part of the retry, using existing protocols. > >There are several advantages to this configuration. One current > >recommendation is to export raw disks from the file server. Some > >storage devices, including I assume Sun's 7000 series, are unable to > >do this. Another is to build two RAID devices on the file server and > >to mirror them with ZFS on the application server. This is also > >sub-optimal as it doubles the space requirement and still does not > >take full advantage of ZFS error checking. Splitting the > >responsibilities works around these problems > > I'm not convinced, but here is how you can change my mind. > > 1. Determine which faults you are trying to recover from. I don't think this has been clearly identified, except that they are ``those faults that are only detected by end-to-end checksums''. > 2. Prioritize these faults based on their observability, impact, > and rate. Perhaps the project should be to extend end-to-end checksums in situations that don't have end-to-end redundancy. Redundancy at the storage layer would be required, of course. -- -Gary Mills- -Unix Support- -U of M Academic Computing and Networking- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
