#2206 Fix the spinning disk on Longhorn

This case requires the creation of a slow virtual disk with dmsetup.

1. Make a slow disk:

   • Make a disk image file: truncate -s 10g slow.img
   • Create a loopback device: losetup --show -P -f slow.img
   • Get the block size of the loopback device: blockdev --getsize /dev/loopX
   • Create slow device: echo "0 <blocksize> delay /dev/loopX 0 500" | dmsetup create dm-slow
   • Format slow device: mkfs.ext4 /dev/mapper/dm-slow
   • Mount slow device: mount /dev/mapper/dm-slow /mnt

2. Build longhorn-engine and run it on the slow disk.

   • make or use a tag from docker hub in next step.
   • docker run --privileged -v /dev:/host/dev -v /proc:/host/proc -v /mnt:/volume longhornio/longhorn-engine:<tag> launch-simple-longhorn slow-vol 10g tgt-blockdev

3. Perform intense I/O on the block device and verify that it doesn’t fail.

   • This uses an iodepth of 16 to maximize the number of threads in tgtd. An iodepth of 16 or more will maximize the number of threads in tgtd. fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=1280k --direct=1 --size=3000m --numjobs=1 --filename=/dev/longhorn/slow-vol --iodepth=16 --verify=sha256
   • This exceeds the number of operations tgtd and longhorn can handle simultaneously. fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=16k --direct=1 --size=10m --numjobs=4 --filename=/dev/longhorn/slow-vol --iodepth=128 --verify=sha256
   • This tests performing one I/O operation at a time: fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=4k --direct=1 --size=10m --numjobs=1 --filename=/dev/longhorn/slow-vol --iodepth=1 --verify=sha256
   • This tests with skipping 4k blocks: fio --name=sparse-writers --ioengine=libaio --rw=write:4k --bs=4k --direct=1 --size=10m --numjobs=1 --filename=/dev/longhorn/slow-vol --iodepth=128 --verify=sha256

4. Perform intense I/O on a filesystem and verify that it doesn’t fail.

   • mkfs.ext4 /dev/longhorn/slow-vol
   • mkdir /slow-mnt
   • mount /dev/longhorn/slow-vol /slow-mnt
   • Run tests similar to the block device tests:
     • fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=1280k --direct=1 --size=3000m --numjobs=1 --filename=/slow-mnt/file.dat --iodepth=16 --verify=sha256
     • fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=16k --direct=1 --size=10m --numjobs=4 --filename=/slow-mnt/file.dat --iodepth=128 --verify=sha256
     • fio --name=random-writers --ioengine=libaio --rw=randwrite --bs=4k --direct=1 --size=10m --numjobs=1 --filename=/slow-mnt/file.dat --iodepth=1 --verify=sha256
     • fio --name=sparse-writers --ioengine=libaio --rw=write:4k --bs=4k --direct=1 --size=10m --numjobs=1 --filename=/slow-mnt/file.dat --iodepth=128 --verify=sha256

5. Repeat with different filesystems, i.e use mkfs.xfs instead of mkfs.ext4.