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Re: Best partition distibution for new install.

On Thu, Nov 20, 1997 at 10:17:22AM -0500,  Raymond A. Ingles wrote:
> On Wed, 19 Nov 1997, robert havoc pennington wrote:
> > 
> > How hard should I try to avoid logical partitions? What's the impact
> > of using them?

AFAIK, under Linux, none whatsoever.

> everything's lost. Splitting things up into separate partitions limits 
> your risk - most likely only one partition at a time will go, and 
> recovery is easier.

Very very true.

> With logical partitions, though, you don't have quite the same protection.
> A single error on the physical partition can hose all the logical
> partitions in it.

Not applicable ; a file system error occurs on a file system. I cannot see
how there could be an error in the physical partition that would affect all
the logical partitions contained therein (except for partition table loss,
of course, but that goes for logical and physical partitions, and recovery
is simple).

>  Then there's the performance question, which, I'm sorry to say, I'm not 
> too clear on. I always thought that the logical partitions were at least 
> physically separate within the partition, [...]

On an MS-DOS compatible file system, most definitely.

> But I've also heard that logical partitions can interleave with each 
> other, like fragmented disk files.

Calls to mind the (really excellent) AIX file system. Not (yet :-( )
applicable under Linux.

>  Well, I've used them before (*way* back when Linux only supported 16MB 
> swap partitions). I made a 32MB physical partition and split it into to 
> 16MB logical partitions. I never noticed any problems from that. 

I have some experience with partitions (otherwise I wouldn't have been so
categorical above).In short, Mess-DOG says you can have 4 main partitions in
the partition table. To circumvent that limit, one of these (called
"extended") can be sub-partitioned with a "logical" partition table
contained in the "extended" partition. The information contained in these
partition tables are, essentially, the beginning cylinder and the size of
the partition. There is therefore no possibility of interleaving partitions
without either further subdividing a partition (writing new device drivers
in the process), or completely leaving the MS-DOS partition system.

Linux, AFAIK, reads in the information, records the beginning and ending
sector of each partition, and that's it. I do not think that Linux, in
acessing the content of partitions, makes any difference whatsoever between
partitions in the primary partition table and the extended partition table
beyond that point.

> > Anyway, I'm hoping to share /home, swap, and /tmp between the two systems.

/home is a good idea.
I don't think /tmp is a good idea, because ISTR /tmp is used and must be
usable before beginning networking. I consider /tmp to be one of the
essential directories, along with /etc and /sbin. Of course, mounting
something on /tmp means that you could have written something before, since
the mount point is a directory ;-)

> > Are there any other directories I can share? Maybe /usr/local? Is this a 
> > good idea in general? Anything I should consider before trying it?
>  If you're going to be installing different versions of packages, you 
> should probably not share any more than the first three. Sharing /usr and 
> /usr/local would mean you'd have a mix of stable and unstable packages, 
> and unless you're careful about it, that could lead to lots of 
> problems.


If you seek to have the _same_ things on on a network (installing one copy
of an executable), it is a good idea. If you seek to have _different_
things (stable and unstable), it is a bad idea. I have no further experience
in this domain, but I imagine you could have a shared fs for things you want
on both, like /usr/local, and the things you want different in /usr.


include <std_disclaim.h>                  Lorens KOCKUM ( kockum@efrei.fr )

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