SLOG / ZIL(Separate Log / ZFS Intent Log)
A fast device that accelerates synchronous writes in ZFS by holding the intent log separately.
A SLOG only helps sync-heavy workloads like NFS for VMs or databases, and it should use power-loss-protected SSDs. For a media NAS it usually makes no difference — don't add one just because you can.
Related articles
ZFS
An advanced filesystem and volume manager offering data integrity, snapshots, compression and software RAID.
NVMe(Non-Volatile Memory Express)
A fast storage interface designed for SSDs, offering much lower latency than SATA.
NFS(Network File System)
A Unix-native network file-sharing protocol offering high performance between Linux systems.