The hyper links didn't work, here are the urls -- http://queue.acm.org/detail.cfm?id=1317400
http://www.sun.com/bigadmin/features/articles/zfs_part1.scalable.jsp#integrity ----- Original Message ----- From: "JZ" <j...@excelsioritsolutions.com> To: "Orvar Korvar" <knatte_fnatte_tja...@yahoo.com>; <zfs-discuss@opensolaris.org> Sent: Sunday, December 28, 2008 7:50 PM Subject: Re: [zfs-discuss] ZFS vs HardWare raid - data integrity? > Nice discussion. Let my chip in my old timer view -- > > Until a few years ago, the understanding of "HW RAID doesn't proactively > check for consistency of data vs. parity unless required" was true. But > LSI had added background consistency check (auto starts 5 mins after the > drive is created) on its RAID cards. Since Sun is primarily selling LSI > HW > RAID cards, I guess at that high level, both HW RAID and ZFS provides some > proactive consistency/integrity assurance. > > HOWEVER, I really think the ZFS way is much more advanced (PiT integrated) > and can be used with other ZFS ECC/EDC features with memory-based data > consistency/inegrity assurance, to achieve an overall considerably better > data availability and business continuity. I guess I just like the > "enterprise flavor" as such. ;-) > > > > > Below are some tech details. -- again, please, do not compare HW RAID with > ZFS at features level. RAID was invented for both data protection and > performance, and there are different ways to do those with ZFS, resulting > in > very different solution architectures (according to the customer segments, > and sometimes it could be beneficial to use HW RAID, e.g. when hetero HW > RAID disks are deployed in a unified fashion and ZFS does not handle the > enterprise-wide data protection......). > > > ZFS does automatic error correction even when using a single hard drive, > including by using end-to-end checksumming, separating the checksum from > the > file, and using copy-on-write redundancy so it is always both verifying > the > data and creating another copy (not overwriting) when writing a change to > a > file. > Sun Distinguished Engineer Bill Moore developed ZFS: > > ... one of the design principles we set for ZFS was: never, ever trust > the > underlying hardware. As soon as an application generates data, we generate > a > checksum for the data while we're still in the same fault domain where the > application generated the data, running on the same CPU and the same > memory > subsystem. Then we store the data and the checksum separately on disk so > that a single failure cannot take them both out. > > When we read the data back, we validate it against that checksum and see > if it's indeed what we think we wrote out before. If it's not, we employ > all > sorts of recovery mechanisms. Because of that, we can, on very cheap > hardware, provide more reliable storage than you could get with the most > reliable external storage. It doesn't matter how perfect your storage is, > if > the data gets corrupted in flight - and we've actually seen many customer > cases where this happens - then nothing you can do can recover from that. > With ZFS, on the other hand, we can actually authenticate that we got the > right answer back and, if not, enact a bunch of recovery scenarios. That's > data integrity." > > See more details about ZFS Data Integrity and Security. > > > Best, > z > > > > ----- Original Message ----- > From: "Orvar Korvar" <knatte_fnatte_tja...@yahoo.com> > To: <zfs-discuss@opensolaris.org> > Sent: Sunday, December 28, 2008 4:16 PM > Subject: Re: [zfs-discuss] ZFS vs HardWare raid - data integrity? > > >> This is good information guys. Do we have some more facts and links about >> HW raid and it's data integrity, or lack of? >> -- >> 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
