On Fri, Jan 15, 2010 at 10:37:15AM -0500, Charles Menser wrote: > Perhaps an ISCSI mirror for a laptop? Online it when you are back > "home" to keep your backup current.
I do exactly this, but: - It's not the only thing I do for backup. - The iscsi initiator is currently being a major PITA for me. http://opensolaris.org/jive/thread.jspa?threadID=121484 This kind of sometimes-attached mirror (whether via iscsi, usb disks, or whatever else) is a useful kind of backup for some circumstances, but it is not much good in others. If your need to recover falls into one of those other circumstances, it can be a bit rough. I like it, because: - It's easy to set up (just a few commands) and (at least ideally) will work basically by itself after that, no thinking required. Those are important characteristics of a good backup! :) - It's reasonably quick to resilver, and reasonably unintrusive; it can make things slower, but doesn't prevent normal use while going. - It can be used for repair, rather than recovery, in the case where the laptop disk develops bad sectors, and maybe therefore avoid more complicaed restores and impact analysis. For recently-written data that hasn't been mirrored, too bad - but it's more likely to happen to older sectors. Scrub regularly overnight with the mirror attached. However, it falls short of the ideal in a number of ways: - In practice you often need to take some action (plug in usb disk, online/offline the component, clear a fault) to kick it off, and/or to prevent hangs and timeouts when moving away. Sometimes you get those anyway (e.g timing out iscsi during zfs import at boot). - ZFS lacks the ability to assign preference or weights to mirrors for read, so running with the mirror attached can often slow the system down, even when not resilvering. - You mirror everything, including all that scratch data that's really not worth backing up, the data you already have replicated elsewhere, and those delete actions you did by mistake. - Restores are tricker and can take multiple steps and thinking, especially if you just want some critical data now. It's hard to know what's in each backup instance. - The size of the backup is tied to the size of the disk - it's more complicated to keep more/older backups than are what is on the primary disk, and tricker to restore to a different-sized disk. I keep snapshots of the backing volume so I can have older images (as well as within the backed-up pool), and if I ever need to look inside an image I clone it before importing on the server. Remember to use import -R! I also zfs send -R my pool to another zfs elsewhere, as a second backup. I have some very Q&D hokey scripts for this (which I want to rewrite and make smarter, now that we have snapshot holds), as do other peeople, but there's not yet quite such an easy setup path for this. I do both things, in the hope that each makes up for the deficiencies of the other. -- Dan.
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