Re: New Linux xfs/reiser file systems

> The "problem" with log based filesystems is that they most likely
> do not know the consequences of a write so an fsync on a file may
> require double writing to both the log and the "real" portion of
> the disk. They can also exhibit the problem that an fsync may
> cause all pending writes to require scheduling unless the log is
> constructed on the fly rather than incrementally.

Yes, this double-writing is a problem. Suppose you have your WAL on a
separate drive. You can fsync() WAL with zero head movement. With a
log based file system, you need two head movements, so you have gone
from zero movements to two.

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026