Before sequential scrub patches ZFS never aggregated I/Os above 128KB. Sequential scrub bumped that to 1MB, which motivation I understand for spinning disks, since it should reduce number of head seeks. But for SSDs it makes much less sense to me, especially on FreeBSD, where due to MAXPHYS limitation device will likely still see bunch of 128KB I/Os instead of one large. Having more strict aggregation limit allows to avoid allocation of large memory buffer and memcpy to/from it, that is a serious problem when bandwidth reaches few GB/s. MFC after: 1 month Sponsored by: iXsystems, Inc. |
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