why separate filesystems?

[Dick Dunn]

carl at p4tustin.UUCP (Carl W. Bergerson) writes:
> 	"Smaller filesystems are faster" - Xenix Installation Guide
> 
> 	This is generally true for all versions of *ix.

This is sort of true in a not-very-useful way.  Smaller file systems can be
faster because the disk arm doesn't have to move as far...but if you've got
80 Mb of data to store, you can't put it in a 50 Mb file system.  What's
more, suppose you've got 80 Mb of data and 120 Mb of space to carve up...
which is better:  divide the data between two 60-Mb file systems or put it
all on one 120-Mb file system?  Answer: use the 120.  Otherwise you'll
spend your time seeking back and forth across the unallocated wasteland at
the end of the first file system to get to the second.

In old free-list style file systems, the scrambling of the free list could
have more of an effect on a larger file system, particularly if you once
filled it pretty full, then dropped way back down below the high-water
mark.

A file system structure which places the most-used data closest together is
going to be faster.

There are various historical reasons for splitting up file systems,
including as has been mentioned, recovery (repairing a damaged file system
was *much* harder before fsck!), size of available disks, etc.
-- 
Dick Dunn     rcd at ico.isc.com -or- ico!rcd       Boulder, CO   (303)449-2870
   ...I'm not cynical - just experienced.