mirror_zfs/module
Allan Jude fc34dfba8e
Fix L2ARC reads when compressed ARC disabled
When reading compressed blocks from the L2ARC, with
compressed ARC disabled, arc_hdr_size() returns
LSIZE rather than PSIZE, but the actual read is PSIZE.
This causes l2arc_read_done() to compare the checksum
against the wrong size, resulting in checksum failure.

This manifests as an increase in the kstat l2_cksum_bad
and the read being retried from the main pool, making the
L2ARC ineffective.

Add new L2ARC tests with Compressed ARC enabled/disabled

Blocks are handled differently depending on the state of the
zfs_compressed_arc_enabled tunable.

If a block is compressed on-disk, and compressed_arc is enabled:
- the block is read from disk
- It is NOT decompressed
- It is added to the ARC in its compressed form
- l2arc_write_buffers() may write it to the L2ARC (as is)
- l2arc_read_done() compares the checksum to the BP (compressed)

However, if compressed_arc is disabled:
- the block is read from disk
- It is decompressed
- It is added to the ARC (uncompressed)
- l2arc_write_buffers() will use l2arc_apply_transforms() to
  recompress the block, before writing it to the L2ARC
- l2arc_read_done() compares the checksum to the BP (compressed)
- l2arc_read_done() will use l2arc_untransform() to uncompress it

This test writes out a test file to a pool consisting of one disk
and one cache device, then randomly reads from it. Since the arc_max
in the tests is low, this will feed the L2ARC, and result in reads
from the L2ARC.

We compare the value of the kstat l2_cksum_bad before and after
to determine if any blocks failed to survive the trip through the
L2ARC.

Sponsored-by: The FreeBSD Foundation
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Allan Jude <allanjude@freebsd.org>
Closes #10693
2020-08-13 23:31:20 -07:00
..
avl Make use of ZFS_DEBUG consistent within kmod sources 2020-07-25 20:07:44 -07:00
icp Prefix zfs internal endian checks with _ZFS 2020-07-28 13:02:49 -07:00
lua lua: Increase reserved stack space for FreeBSD in debug config 2020-07-31 09:17:37 -07:00
nvpair Prefix zfs internal endian checks with _ZFS 2020-07-28 13:02:49 -07:00
os Release onexit/events with any missed zfsdev_state 2020-08-13 15:03:23 -07:00
spl Cleanup linux module kbuild files 2020-06-10 09:24:15 -07:00
unicode Prefix zfs internal endian checks with _ZFS 2020-07-28 13:02:49 -07:00
zcommon Refactor ccompile.h to not include system headers 2020-07-25 20:09:50 -07:00
zfs Fix L2ARC reads when compressed ARC disabled 2020-08-13 23:31:20 -07:00
.gitignore Cleanup linux module kbuild files 2020-06-10 09:24:15 -07:00
Kbuild.in Move zfs_gitrev.h to build directory 2020-06-24 18:19:28 -07:00
Makefile.bsd Prefix zfs internal endian checks with _ZFS 2020-07-28 13:02:49 -07:00
Makefile.in Include FreeBSD sources in module dist 2020-06-26 14:19:35 -07:00