Eric Schrock wrote:
On May 19, 2009, at 8:56 PM, Nicholas Lee wrote:
So txg is sync to the slog device but retained in memory, and then
rather than reading it back from the slog to memory it is copied to
the pool from memory the copy?
Yes, that is correct. It is best to think of the ZIL and the txg sync
process as orthogonal - data goes to both locations at different
times. The ZIL (technically "all ZILs" since they're per-filesystem)
is *only* read in the event of log replay (unclean shutdown). During
normal operation it is never read. Hence the benefit of write-biases
SSDs - it doesn't matter if reads are fast for slogs.
Yes. OTOH we also know that if the pool is exported, then there
is nothing to be read from the slog. So in the case of a properly
exported pool, we should be allowed to import sans slog. No?
I seem to recall an RFE for this, but can't seem to locate it now.
-- richard
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