I'm testing a new TrueNAS build for eventual use as an ESXi iSCSI datastore. I was testing the following pool configurations and found some surprising results:
- 2 Intel P5510 3.84TB mirrored + no SLOG
- 2 Intel P5510 3.84TB mirrored + 1 Intel P5510 3.84TB as SLOG
- Sequential writes: "No SLOG" config is 20-31% faster
- Random writes: "No SLOG" config is 6-55% faster
- Sequential writes: "No SLOG" config is 23-53% faster (probably even faster but my 2x10GbE NICs are a bottleneck here)
- Random writes: "No SLOG" config is about the same
- Both pools were set up with sync=always, compression=lz4, atime=off, recordsize=128K, volblocksize=64K
- Windows tests used CrystalDiskMark 8.0.2 in "NVMe SSD" mode
- Fio tests were created that mimic the above CDM tests
- I'm not planning on using a P5510 as a SLOG drive in production but that's what I had on hand to test with.