Anton B. Rang wrote: > Some RAID systems compare checksums on reads, though this is usually only for > RAID-4 configurations (e.g. DataDirect) because of the performance hit > otherwise. >
For the record, Solaris had a (mirrored) RAID system which would compare data from both sides of the mirror upon read. It never achieved significant market penetration and was subsequently scrapped. Many of the reasons that the market did not accept it are solved by the method used by ZFS, which is far superior. > End-to-end checksums are not yet common. The SCSI committee recently ratified > T10 DIF, which allows either an operating system or application to supply > checksums and have them stored and retrieved with data. Oracle has been > working to add support for this to Linux, and several array and drive vendors > have committed to implementing it. So one could say that ZFS is ahead of the > curve here. > Oracle also has data checksumming enabled by default for later releases. I look forward to any field data analysis they may publish :-) > ZFS is not particularly revolutionary: software RAID has been around since > the invention of the term; end-to-end checksums to disk have been used since > the 1960s (though more often in databases, tape, and optical media); > WAFL-like file structures may pre-date NetApp. It does put these together for > the first time in a widely available system, though, which is certainly > innovative and useful. It will be more useful when it has a more complete > disaster recovery model than 'restore from backup.' > If you wish to implement a disaster recovery model, then you should look far beyond what ZFS (or any file system) can provide. Effective disaster recovery requires significant attention to process. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
