Evolving Ext4 for Shingled Disks.

Drive-Managed SMR (Shingled Magnetic Recording) disks offer a plug-compatible higher-capacity replacement for conventional disks. For non-sequential workloads, these disks show bimodal behavior: After a short period of high throughput they enter a continuous period of low throughput. We introduce ext4-lazy, a small change to the Linux ext4 file system that significantly improves the throughput in both modes. We present benchmarks on four different drive-managed SMR disks from two vendors, showing that ext4-lazy achieves 1.7-5.4× improvement over ext4 on a metadata-light file server benchmark. On metadata-heavy benchmarks it achieves 2-13× improvement over ext4 on drive-managed SMR disks as well as on conventional disks.