Write Amplification

SSD considerations.

What it is

Bytes written to physical storage per byte of application data. Higher than 1 due to filesystem overhead, journals, indexes, replication.

SSDs care: each write reduces SSD lifetime. High amplification shortens lifespan.

Modern SSDs handle amplification via wear levelling. The OS and filesystem still affect total write volume.

Sources

Filesystem journals: writes happen twice (journal then final).

Database WALs: writes go through the write-ahead log first.

Replication: each write goes to multiple copies.

Measuring

iostat or per-device metrics: total bytes written.

Application metrics: bytes accepted from clients.

Ratio of the two = amplification factor.

Reducing amplification

Larger batch sizes reduce per-write overhead.

Compression: smaller logical writes, smaller physical writes.

Modern filesystems (ZFS, btrfs) handle amplification differently from older ones; choose appropriately.