Path: utzoo!attcan!uunet!ibmpa!bass.tcspa.ibm.com!webb
From: webb@bass.tcspa.ibm.com (Bill Webb)
Newsgroups: comp.sys.ibm.pc.rt
Subject: Re: Non-standard partition sizes, files lost
Message-ID: <4682@ibmpa.UUCP>
Date: 27 Mar 90 23:28:59 GMT
References: <8603@lindy.Stanford.EDU>
Sender: news@ibmpa.UUCP
Organization: IBM AWD Paloalto
Lines: 68

>...
> hd1 was therefore re-partitioned to the standard root configuration.
> Both hard drives now have exactly the same partition sizes.
> So far, so good.  No data has been lost from hd1g since the
> re-partitioning.
> 
> So, does anybody have any suggestion/advice to offer?  Should I have
> trusted the author of one of my books who warned me to set up both
> my disks the same?  If so, why is there a "standard source" option
> under minidisk?  Does the very existence of hd1b cause the system
> to want to use it for swap space, and if so, does the swapper assume
> that hd0b and hd1b are the same size?  Did my use of dd cause any
> problems?
> 

I don't have any constructive suggestions but I hope I can at least 
answer some of your questions. 

There should be no need to have all swap partitions the same size, though
the original BSD 4.2 and 4.3 documentation assumed that they were (since
the partition sizes were hard coded into the driver). We (IBM) added 
the minidisk stuff so that partition sizes could be changed and for 
compatibility and coexistance with AIX. If the sizes are wildly different
then you tend to waste some kernel resources in the maps that keep track
of swap space utilization and don't spread the paging evenly over several
drives but these are secondary effects.

In order to use more than one swap partition it must both be configured into
your kernel and you must start swapping on it with a swapon (there is a 
swapon -a in /etc/rc so all that is really required in addition to the kernel
	/dev/hd1b /swap swap sw 0 0
in /etc/fstab. Until a swapon is done you only swap on the first swap
device configured into your kernel.

One machine I looked at here used hd0b, hd1b, hd2b, and sc0b as swap 
devices, they had 19355, 45080, 152615, and 66896 blocks of swap space
respectively (that was the machine we used to test to see if we could
malloc 128MB if I remember correctly). This system does not have problems
with trashing filesystems.

Your use of dd should not have cause problems as the kernel will check to 
make sure that you don't go outside of a partition.

I cannot explain your problems unless it is possible that you failed 
to reboot the machine after changing the partitions with minidisk. If
you didn't reboot then you could definitely could have had problems as
the new partitions don't take effect until after a reboot and mkfs
and newfs would have affected the old partitions only. Even then though
I don't think you would have gotten the symptoms that you did, so I'm 
at a loss to explain what happened.

Since you've since gotten it to work by repartitioning we may never 
know what the actual problem was.

> Sorry for the length of my query.  Hope the feedback I get will be
> educational for the newsgroup.  Thanks.
> 
> -- Richard Anderson                 cn.rna@forsythe.stanford.edu
>    Systems Department, Green Library
>    Stanford, CA 94305-6004               (415) 725-7932

I hope I've been able to answer at least some of the queries.

----------------------------------------------------------------

The above views are my own, not necessarily those of my employer.
Bill Webb (IBM AWD Palo Alto), (415) 855-4457.
UUCP: ...!uunet!ibmsupt!webb