From 20% to 5%: How Modern ZFS Changed the Free Space Debate
1 min read
Summary
For years, ZFS users have operated under the 80% rule, whereby pool sizes should never exceed this figure to avoid poor performance, fragmentation and system issues,
This mantra was born from the metaslab allocator which formerly triggered a slower, more fragmented approach to allocation below the 20% threshold,
ZFS copy-on-write filesystem also meant data had to be written to new blocks before the old ones were marked as free,
However, ZFS veterans now believe that modern ZFS optimizer, smarter space management and larger drives mean the figure should be closer to 5-10% free space for optimal performance.
It is stressed that the dropout of the rule should be done gradually and with great caution.