> If you could start with a 3 drive zraid2 as the underlying pool > storage and later add drives to the existing zraid2 as space was > needed, then ZFS would be the ultimate FS (at least for me). > > Any takers? How hard would this be? You can do something like this: zpool create foo raidz2 dev0 dev1 dev2 dev3 zpool add foo raidz2 dev4 dev5 dev6 dev7 The new devices are in a different raidz2 group but but *all of the space* will be used for any filesystem on this pool -- isn't this good enough and if not, why? If you add a new disk to the same raid, you have to redistirbute most data. Not worth it Note you need at least 3 disks for raidz and 4 disks for raidz2. In general you want to put almost all your disks in a single pool but not in a single mirror, raidz or raidz2. Root zfs should be in its own pool and perhaps databases. See http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"

> > zpool create foo raidz2 dev0 dev1 dev2 dev3 > > zpool add foo raidz2 dev4 dev5 dev6 dev7 > > > > The new devices are in a different raidz2 group but but *all > > of the space* will be used for any filesystem on this pool -- > > isn't this good enough and if not, why? > > Isn't it obvious? > > You waste less diskspace. In the above setup you are only using > half your diskspace and depending on what you need it for you might > aswell have been using a mirror... > > Often having two parity drives can be more important than the ratio of > parity vs. non-parity. Fair enough. > Also, if you DO want 50% parity, a single raidz2 with 8 drives with 50% > parity is more resilient to failures than 2x4 raidz2 since any 4 drives > can fail whereas in the latter case any 2 drives can fail, or up 4 > drives if they happen to be the right drives. 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. > > Not worth it > > Most definitely worth it in many situations where performance is just > not the goal. So what if it takes a week to perform the operation, as > long as the array is not degraded during this timewindow. It is not obvious at all that performance would not be a goal for a freebsd user! 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*. Even you may care about the array being down for hours/days! Thinking more about this, I believe this can be done without adding too many complications. Proof left as an exercise:-) _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"