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
