> Are there benchmarks somewhere showing a RAID10 > implemented on an LSI card with, say, 128MB of cache > being beaten in terms of performance by a similar > zraid configuration with no cache on the drive > controller? > > Somehow I don't think they exist. I'm all for data > scrubbing, but this anti-raid-card movement is > puzzling.
Oh, for joy - a chance for me to say something *good* about ZFS. rather than just try to balance out excessive enthusiasm. Save for speeding up synchronous writes (if it has enough on-board NVRAM to hold them until it's convenient to destage them to disk), a RAID-10 card should not enjoy any noticeable performance advantage over ZFS mirroring. By contrast, if extremely rare undetected and (other than via ZFS checksums) undetectable (or considerably more common undetected but detectable via disk ECC codes, *if* the data is accessed) corruption occurs, if the RAID card is used to mirror the data there's a good chance that even ZFS's validation scans won't see the problem (because the card happens to access the good copy for the scan rather than the bad one) - in which case you'll lose that data if the disk with the good data fails. And in the case of (extremely rare) otherwise-undetectable corruption, if the card *does* return the bad copy then IIRC ZFS (not knowing that a good copy also exists) will just claim that the data is gone (though I don't know if it will then flag it such that you'll never have an opportunity to find the good copy). If the RAID card scrubs its disks the difference (now limited to the extremely rare undetectable-via-disk-ECC corruption) becomes pretty negligible - but I'm not sure how many RAIDs below the near-enterprise category perform such scrubs. In other words, if you *don't* otherwise scrub your disks then ZFS's checksums-plus-internal-scrubbing mechanisms assume greater importance: it's only the contention that other solutions that *do* offer scrubbing can't compete with ZFS in effectively protecting your data that's somewhat over the top. - bill This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
