Disk Layout/Partitioning Practices

Tom Mitchell mitch48 at sbcglobal.net
Sat Jan 31 17:45:15 UTC 2004


On Wed, Jan 28, 2004 at 11:34:19AM -0500, Kent Borg wrote:
> On Wed, Jan 28, 2004 at 03:44:14PM +0000, Alan Dunkley wrote:
> > On Wednesday 28 Jan 2004 3:01 pm, Ron Herardian wrote:
> > > When installing everything and allowing for future updates and packages I
> > > am using the following disk layout:
> > >
> > > 	Mount Point	Size
> > > 	/boot		100MB
> > > 	/		500MB
> > > 	/usr		4GB
> > > 	/var		2GB
> > > 	swap		2x physical RAM, e.g., 1GB
> > > 	/home		TBD, e.g., 1GB per user
> > >         /opt		TBD/catchall [3rd party servers will be installed here]
> 
> A couple suggestions:
> 
> Swap: Just use 1 GB.  It is big enough to be significant from a RAM
> perspective, but it is still small and cheap in terms of disk sizes.

This is a good place to start unless you have experience otherwise.

> Put a lot of physical RAM in your machine, certainly.

Yes, Yes, Yes...  DRAM....

Remember that Linux supports swap to files.  If you need more swap space
for a project you can add swap files at a later time.

You do want enough DRAM + swap to permit your largest processes to do
common things like "fork(); exec()" and not have the kernel return
errors for want of virtual resources.

Today DRAM is inexpensive and "disk-speed to DRAM-speed" ratios so
large that you do not want much if any swap IO.  With modern VM
systems and concepts like shared pages, copy on write etc... the key
value for a 'big' swap is kernel book keeping.  The kernel must
believe that it has has enough backing store in case you "touch"
the pages the process requested.

I happen to like testing various bounds and limits so my swap space is
big.  Big enough for two run away big processes (~6GB).  In practice
this is way too large and when swapping the box is worthless for
interactive work.

The classic 2xDRAM, 4xDRAM, 8xRAM swap rules had a lot to do with the
balance of DRAM cost (expensive) to disk cost to system usefulness.

Today time slices are very short. When time slices are compared to
disk access time extensive swap IO does not make sense.  When the
effective runtime for a set of pages is larger than the disk IO time
and overhead it can make sense.  See stuff like job control, Ctl-Z
stop, checkpoint and restart.  On an interactive workstation swap IO
does not make much sense.

-- 
	T o m  M i t c h e l l 
	mitch48-at-sbcglobal-dot-net





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