--- wikisrc/zfs.mdwn	2021/02/14 15:07:29	1.31
+++ wikisrc/zfs.mdwn	2021/02/14 16:35:50	1.32
@@ -35,6 +35,20 @@ likely best served by the most recent ve
 branch.  As of 2021-02, ZFS in the NetBSD 9.1 release is very close to
 netbsd-9.
 
+### Native blocksize
+
+ZFS attempts to find out the native blocksize for a disk when using it
+in a pool; this is almost always 512 or 4096.  Somewhere between 9.0
+and 9.1, at least some disks on some controllers that used to report
+512 now report 4096.  This provokes a blocksize mismatch warning.
+
+Given that the native blocksize of the disk didn't change, and things
+seemed OK using the 512 emulated blocks, the warning is likely not
+critical.  However, it is also likely that rebuilding the pool with
+the 4096 blocksize is likely to result in better behavior because ZFS
+will only try to do 4096-byte writes.  \todo Verify this and find the
+actual change and explain better.
+
 ## NetBSD-current
 
 NetBSD-current (as of 2021-02) has similar ZFS code to 9.