[EMAIL PROTECTED] wrote: >>> If you care enough to do backups, at least care enough to be >>> able to restore. For my home backups, I use portable drives with >>> copies=2 or 3 and compression enabled. I don't fool with >>> incrementals, but many people do. The failure mode I'm worried >>> about is decay, as the drives will be off most of the time. The >>> copies feature works well for this failure mode. >>> >> I am definitely and strongly interested in restoring! That's why I hate >> my previous backup solutions so much (NTI backup and then Acronis True >> Image); I verified backups and tested restores, and had *FAR* too much >> trouble to be at all comfortable. The photos and the ebooks are backed >> up eventually (but not always within the month) to good DVDs, and one >> copy is kept off-site, and that's the stuff I'd miss most if it went, >> but I want a good *overall* solution. >> >> The "copies" thing sounds familiar from discussion here...ah. Yes, >> that's exactly perfect; it lets me make up a batch of miscellaneous >> spare disks totaling enough space, each one a vdev, put them into one >> pool (no redundancy), but with copies=2 get nearly the redundancy of >> mirroring which would have required matching drives. At least, if I >> > > >From what I have seen I think you are over estimating the value of > copies=x. copies=X are guaranteed to store multiple copies (X) of the > blocks _somewhere_ in the pool, but not necessarily on different disks. > So while you may gain mirror like protection when you have failed blocks on > a disk (maybe -- blocks could be too close together on the same disk); you > do not necessarily gain that from a failed disk (block copies could be on > only one disk). Having different sized unprotected disks and using copies=N > has less mirror like effect over time and fragmentation of those disks. > > http://blogs.sun.com/bill/entry/ditto_blocks_the_amazing_tape > http://blogs.sun.com/relling/entry/zfs_copies_and_data_protection >
Yes, that's quite clear even just from the man page. That's why I said "nearly"; I understand that "copies < mirrors", as you put it. Not *necessarily* on different disks, but it *tries* to put it on different disks. "Over time" isn't necessarily an issue, since a new full backup could be done into a clean filesystem. -- David Dyer-Bennet, [EMAIL PROTECTED]; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
