Reserved block count for Large Filesystem-蒲公英云

Reserved block count for Large Filesystem

Q:
On large FS like 100gb default value of “Reserved block count” takes 5% of usable disk, can this value be safely changed to 1% and not affect a performance ? Is a reservation size of 1gb enough for 100gb disk ? And when we have even larger filesystem like 1Tb default “Reserved block count” is 50GB, is it an absolutely minimum must have reserved number of space for disk performance, or it’s just a legacy concept which can be adjusted?

A:
If you set the reserved block count to zero, it won’t affect performance much except if you run for long periods of time (with lots of file creates and deletes) while the filesystem is almost full (i.e., say above 95%), at which point you’ll be subject to fragmentation problems. Ext4’s multi-block allocator is much more fragmentation resistant, because it tries much harder to find contiguous blocks, so even if you don’t enable the other ext4 features, you’ll see better results simply mounting an ext3 filesystem using ext4 before the filesystem gets completely full. If you are just using the filesystem for long-term archive, where files aren’t changing very often (i.e., a huge mp3 or video store), it obviously won’t matter.