Alexander Skwar wrote: > Okay. This contradicts the ZFS Best Practices Guide, > which states: > > # For production environments, configure ZFS so that > # it can repair data inconsistencies. Use ZFS > redundancy, > # such as RAIDZ, RAIDZ-2, RAIDZ-3, mirror, or copies > > 1, > # regardless of the RAID level implemented on the > # underlying storage device. With such redundancy, > faults in the > # underlying storage device or its connections to the > host can > # be discovered and repaired by ZFS. <snip> > Anyway. Without redundancy, ZFS cannot do recovery, > can > it? As far as I understand, it could detect block > level corruption, > even if there's not redundancy. But it could not > correct such a > corruption. > > Or is that a wrong understanding? > > If I got the gist of what you wrote, it boils down to > how reliable > the SAN is? But also SANs could have "block level" > corruption, > no? I'm a bit confused, because of the (perceived?) > contra- > diction to the Best Practices Guide… :)
This comes down to how much you trust your "storage device" whatever that may be. If you have full faith in your SAN (and I don't have full faith in it, no matter what its make/model), then ignore ZFS redundancy. When I first deployed a hardware RAID solution around 1995, the vendor proudly stated that the device could scrub mirrors and correct errors. I asked when it found a discrepancy, how did it know which side of the mirror was correct? He stammered for a while, but it basically came down to the device flipping a coin. ZFS will ensure integrity, even when the underlying device fumbles. When you mirror the iSCSI devices, be sure that they are configured in such a way that a failure on one iSCSI "device" does not imply a failure on the other iSCSI device. As a simple example, if you sliced a disk into three partitions and then presented them as a three way mirror to ZFS, then a single disk failure will wipe out everything, even though you have the illusion of redundancy at the ZFS level. I have seen some systems where the SAN has presented what appeared to be independent devices, but a failure on the underlying disk faulted both devices, rendering ZFS helpless. Good luck, Marty -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
