On Sun, Nov 1, 2015 at 11:44 PM, Thijs Cramer <[email protected]> wrote:
> Hi guys, > > Recently in a discussion online, i discussed the new Seagate 8TB SMR disks > in combination with ZFS. > A big point that was undecided was: Can a SLOG help during rebuild of a > bit SMR disk based array? > > I know it's more risky to use the SLOG for resilver activities, but > rebuilding sequentially could benefit these disks insanely. The problem > with these disks is that under heavy load, the disk because very slow on > random writes because of the SMR rewrites the disk has to do. > > Can anyone answer whether it's currently beneficial to have a SLOG on an > SMR disk array, or answer whether it's easy to adapt the code a bit to make > this happen? > > Currently, the ZIL (and thus log devices / SLOG) is not involved in resilvering. Therefore adding a SLOG device will have no impact on resilver speed. (Though I guess there could be secondary effects if adding the SLOG reduces fragmentation in the main devices.) If you have a specific proposal for how the ZIL / SLOG could be used to accelerate resilvering, I can give you feedback on its feasibility. --matt
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