> I believe raidz2 means two parity blocks so if you want 50% > parity you'd need raidz4. But that nit aside, you have a > valid point. Yes, sorry. I was kind of continuing a train of thought I have had previously that was not specific to raidz2. > It is not obvious at all that performance would not be a goal > for a freebsd user! Of course most people care somewhat for performance, but sometimes you truly are not really that interested in getting better performance than say a single disk. That is, performance is not always the goal of setting up a raids, even if it will always be a nice bonus. > It *is* obvious that you would want more space but not obvious > how to do the conversion from an N disk raidz2 array to N+1 > disk raidz2 array *without bringing the whole array down*. I realize it is not trivial to implement; but I do mean that even if performance is adversely affected for an extended period of time, being able to *do* the conversion at all is often very useful. And even if it has to be be brought offline, that's still better than not being able to do it at all... > Even you may care about the array being down for hours/days! ... but yes, that will be annoying in almost any circumstance. :) > Thinking more about this, I believe this can be done without > adding too many complications. Proof left as an exercise:-) With a traditional raid5/6 it shouldn't be too hard doing a hare/tortoise re-write from beginning to end provided that you have reserved some bit of space on the underlying disks for being able to do this in a crash-safe manner - or am I missing something? In practice I can imagine that it quickly gets complicated of course; especially supporting it online. If nothing else, the fact that most implementations don't support this is probably saying something :) Wonder if raidz/raidz2 will allow striping to vary on a per-stripe basis. If so, should it perhaps be just a matter of re-writing the entire tree with the new disk in place? But then perhaps snapshots/clones will complicate matters. Come to think of it, I think this was already discussed on zfs-discuss. -- / Peter Schuller PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller_at_infidyne.com>' Key retrieval: Send an E-Mail to getpgpkey_at_scode.org E-Mail: peter.schuller_at_infidyne.com Web: http://www.scode.org
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