> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Jim Klimov
> And regarding the "considerable activity" - AFAIK there is little way
> for ZFS to reliably read and test "TXGs newer than X"
My understanding is like this: When you make a snapshot, you're just creating
a named copy of the present latest TXG. When you zfs send incremental from one
snapshot to another, you're creating the delta between two TXG's, that happen
to have names. So when you break a mirror and resilver, it's exactly the same
operation as an incremental zfs send, it needs to calculate the delta between
the latest (older) TXG on the previously UNAVAIL device, up to the latest TXG
on the current pool. Yes this involves examining the meta tree structure, and
yes the system will be very busy while that takes place. But the work load is
very small relative to whatever else you're likely to do with your pool during
normal operation, because that's the nature of the meta tree structure ... very
small relative to the rest of your data.
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