zfsonlinux/zfs — pull request #589 by nedbass (2012-02-29 19:48:21+00:00)
Title: Align parition end on 1 MiB boundary

Some devices have exhibited sensitivity to the ending alignment of
partitions. In particular, even if the first partition begins at 1
MiB, we have seen many sd driver task abort errors with certain SSDs
if the first partition doesn't end on a 1 MiB boundary. This occurs
when the vdev label is read during pool creation or importation and
causes a delay of about 30 seconds per device. It can also be
simulated with dd when the pool isn't imported:

dd if=/dev/sda1 of=/dev/null bs=262144 count=1

For the record, this problem was observed with SMARTMOD
SG9XCA2E200GE01 200GB SSDs. Unfortunately I don't have a good
explanation for this behavior. It seems to have something to do with
highly fragmented single-sector requests being issued to the device,
which it may not support. With end-aligned partitions at least
page-sized requests were queued and issued to the driver according
to blktrace. In any case, aligning the partition end is a fairly
innocuous work-around, wasting at most 1 MiB of space.

Issue #574