CI: run ztest on compressed zpool

When running ztest under the CI a common failure mode is for the
underlying filesystem to run out of available free space.  Since
the storage associated with a GitHub-hosted running is fixed, we
instead create a pool and use a compressed ZFS dataset to store
the ztest vdev files.  This significantly increases the available
capacity since the data written by ztest is highly compressible.
A compression ratio of over 40:1 is conservatively achieved using
the default lz4 compression.  Autotrimming is enabled to ensure
freed blocks are discarded from the backing cipool vdev file.

Lastly, the default zloop run time is increased to an hour or
up to 12 iterations, and each individual ztest run is increased
to 5 minutes.

Signed-off-by: Brian Behlendorf <[email protected]>

Author: behlendorf

.github/workflows/zloop.yml

@@ -40,10 +40,9 @@ jobs:
         sudo modprobe zfs
     - name: Tests
       run: |
-        sudo mkdir -p $TEST_DIR
-        # run for 10 minutes or at most 6 iterations for a maximum runner
-        # time of 60 minutes.
-        sudo /usr/share/zfs/zloop.sh -t 600 -I 6 -l -m 1 -- -T 120 -P 60
+        truncate -s 1T /var/tmp/vdev
+        sudo zpool create cipool -m $TEST_DIR -O compression=on -o autotrim=on /var/tmp/vdev
+        sudo /usr/share/zfs/zloop.sh -t 3600 -I 12 -l -m 1 -- -T 300 -P 60
     - name: Prepare artifacts
       if: failure()
       run: |