4 ms·
Out of the box configuration for most journaling filesystems only journal metadata not data. Journaling data cuts write throughput in half and it’s not necessa
by arielweisberg 6y ago
Out of the box configuration for most journaling filesystems only journal metadata not data.
Journaling data cuts write throughput in half and it’s not necessary most of the time.
- throwaway8941 6y agoIt's worthy of note that log-structured and copy-on-write filesystems (which I've seen described as two types of journaling) like btrfs and F2FS log data as part of their normal operation without any performance loss, so you always get a consistent view of the filesystem (barring bugs in the FS code or fsync-is-not-really-an-fsync treachery from your hardware).
- sedatk 6y agoAs long as writes are flushed sequentially, I see no problem with metadata only journaling, but apparently, NVMe's don't provide such guarantees.
- arielweisberg 6y agoYou don’t get a guarantee of write ordering from not just the disk (pretty much any kind) but the OS IO scheduler. Journaling filesystems can still implement atomic appends with only metadata journaling. Updating in place is generally not atomic because of the way writeback works for buffered IO. If you use unbuffered IO you bypass the OS scheduler but still have the disk reordering things if you don’t use write barriers and they still don’t guarantee atomicity for regular writes.