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Hello, I have several ~12TB storage servers using Solaris with ZFS. Two of them have recently developed performance issues where the majority of time in an spa_sync() will be spent in the space_map_*() functions. During this time, "zpool iostat" will show 0 writes to disk, while it does hundreds or thousands of small (~3KB) reads each second, presumably reading space map data from disk to find places to put the new blocks. The result is that it can take several minutes for an spa_s...