On Mon, May 21, 2012 at 09:18:03PM -0500, Bob Friesenhahn wrote: > On Mon, 21 May 2012, Jim Klimov wrote: >> This is so far a relatively raw idea and I've probably missed >> something. Do you think it is worth pursuing and asking some >> zfs developers to make a POC? ;) > > I did read all of your text. :-) > > This is an interesting idea and could be of some use but it would be > wise to test it first a few times before suggesting it as a general > course.
I've done basically this kind of thing before: dd a disk and then scrub rather than replace, treating errors as expected. > Zfs will try to keep the data compacted at the beginning of the > partition so if you have a way to know how far out it extends, then the > initial 'dd' could be much faster when the pool is not close to full. zdb will show you usage per metaslab, you could use that and effectively select offset ranges to skip any empty ones. After a while, and once the pool has seen usage fill past low %'ages, I'd say most metaslabs would have some usage, so you might not save much time. Going to finer detail within a metaslab is not worthwhile - much more involved and involves the seeks you're trying to avoid. -- Dan.
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