Alexander Motin 37f6845c6f Improve too large physical ashift handling ... When iterating through children physical ashifts for vdev, prefer ones above the maximum logical ashift, that we can actually use, but within the administrator defined maximum. When selecting top-level vdev ashift, do not set it to the defined maximum in case physical ashift is even higher, but just ignore one. Using the maximum does not prevent misaligned writes, but reduces space efficiency. Since ZFS tries to write data sequentially and aggregates the writes, in many cases large misanigned writes may be not as bad as the space penalty otherwise. Allow internal physical ashifts for vdevs higher than SHIFT_MAX. May be one day allocator or aggregation could benefit from that. Reduce zfs_vdev_max_auto_ashift default from 16 (64KB) to 14 (16KB), so that ZFS may still use bigger ashifts up to SHIFT_MAX (64KB), but only if it really has to or explicitly told to, but not as an "optimization". There are some read-intensive NVMe SSDs that report Preferred Write Alignment of 64KB, and attempt to build RAIDZ2 of those leads to a space inefficiency that can't be justified. Instead these changes make ZFS fall back to logical ashift of 12 (4KB) by default and only warn user that it may be suboptimal for performance. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes #13798		2022-09-08 10:30:53 -07:00
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spl.4	Replace dead opensolaris.org license link	2022-07-11 14:16:13 -07:00
zfs.4	Improve too large physical ashift handling	2022-09-08 10:30:53 -07:00