Why is restore so slow?

[Larry McVoy]

I believe that a key component to the slowness of restore is the synchronous
nature of directory operations in the Unix file system.  For example, a create,
something that occurs quite often in restore :-), is synchronous.  It has to
be, those are the semantics of a Unix file system (can you say lock files?).
It actually has to be atomic and completed when the system call returns to the
user, the fact that it is synchronous is an implementation issue that has been
much discussed in comp.arch; I took the point of view that it was a "good thing"
and somebody from Japan took the point of view that it was "too slow".  Before
everyone starts complaining, think back to the days that you had to repair
file systems with fsdb (remember that? If not, be quiet).

The correct fix, in my opinion, is hardware, not software.  Use NVRAM and reclaim
the directory pages from that.  The semantics remain and you get the performance
back.
---
Larry McVoy, Sun Microsystems     (415) 336-7627       ...!sun!lm or lm at sun.com