>>>>> "t" == Tim <t...@tcsac.net> writes:
t> couldn't you simply do a detach before removing the disk, and
t> do a re-attach everytime you wanted to re-mirror?no, for two reasons. First, when you detach a disk, ZFS writes something to the disk that makes it unrecoverable. The simple-UI wallpaper blocks your access to the detached disk, so you have no redundancy while detached. In this thread is a workaround to disable the checks (AIUI they're explaining a more fundamental problem with a multi-vdev pool because you can't detach one-mirror-half of each vdev at exactly the same instant, but multi-vdev is not part of Niall's case): http://opensolaris.org/jive/thread.jspa?threadID=58780 second, when you attach rather than online/clear/notice-its-back, ZFS will treat the newly-attached disk as empty and will resilver everything, not just your changes. It's the difference between taking 5 minutes and taking all night. and you don't have redundancy until the resilver finishes. Another interesting question is: (1) unplug the home USB disk (2) write to the internal laptop disk (3) retach the USB disk and start resilvering (the quick-resilver, not the newly-attached resilver) (a) laptop disk goes bad. maybe a bunch of UNC's are uncovered during the resliver. This is pretty plausible. Plausible how? maybe you've been running without making backup for weeks, and then your machine started acting goofy so you said ``shit! i haven't backed up! i better do it now if I still can.'' you just plugged in because the laptop disk was _starting_ to go bad, and then it did. (b) system freezes and has to be hard-reset during the resilver (c) maybe after reboot you try again. eventually you give up on the laptop disk and decide to lose your last month of changes. you just want your data back as of the last backup, and a working machine. (4) what's the status of the home USB disk after these partial-resilvers? `no valid replicas', or it works? My impression is, at least sometimes or even usually, it will work. Is it guaranteed to always work, though? Ordinary manual backups DO tolerate this scenario: if your machine breaks while writing this week's incremental, you can still restore by reading last week's incremental. I remember AVS/ii had a brittle but planned scheme for this scenario, too: * First, there is always a resilver source and target---for better or worse, it's not an ambiguous merging operation like ZFS. * Second, before starting the resilver, you take an ii (device-level snapshot) of the resilver target. The resilver is done UNsafely, but if it stops mid-way, you can roll back to the pre-resilver snapshot and get back the working home/target disk you had in (1). SVM and Linux-LVM2 and most RAID-like mirrors do NOT handle this scenario gracefully.
pgp8aF1fodWqv.pgp
Description: PGP signature
_______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
