[Bug 191808] New: zfs trim_on_init should trim in smaller chunks

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191808

            Bug ID: 191808
           Summary: zfs trim_on_init should trim in smaller chunks
           Product: Base System
           Version: 10.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: Needs Triage
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: michael at supermathie.net

System: FreeBSD fearless2 10.0-RELEASE-p7 FreeBSD 10.0-RELEASE-p7 #0: Wed Jul 9
12:19:19 EDT 2014 root at fearless2:/usr/obj/usr/src/sys/CAMDEBUG amd64

I have an IBM server configured with 400GB SAS SSDs on which I'm trying to
create a ZFS pool.

# zpool create tank da1 da2 da3 da4

By default, ZFS will trim/unmap the drive when configuring but the UNMAP
command takes
78s to complete, longer than kern.cam.da.default_timeout (60).

I get timeouts and it tries to resubmit but will never finish:
Jul  9 12:40:06 fearless2 kernel: (da1:mps0:0:3:0): UNMAP. CDB: 42 00 00 00 00
00 00 00 18 00
Jul  9 12:41:06 fearless2 kernel: (da1:mps0:0:3:0): UNMAP. CDB: 42 00 00 00 00
00 00 00 18 00 length 24 SMID 623 command timeout cm 0xfffffe00010c11b0 ccb
0xfffff80028931000
Jul  9 12:41:06 fearless2 kernel: (noperiph:mps0:0:4294967295:0): SMID 1
Aborting command 0xfffffe00010c11b0
Jul  9 12:41:07 fearless2 kernel: (da1:mps0:0:3:0): UNMAP. CDB: 42 00 00 00 00
00 00 00 18 00
Jul  9 12:41:07 fearless2 kernel: (da1:mps0:0:3:0): CAM status: Command timeout

Increasing kern.cam.da.default_timeout to 90s allows the command to finish and
the pool to be created.

ZFS should probably UNMAP smaller chunks at a time (4GB?) on initial creation
so the
command can complete in a timely manner. Or, can it submit the UNMAP request
with a much higher than normal timeout?

Note that vfs.zfs.vdev.trim_max_bytes doesn't apply here.

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