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Re: fdisk, parted, problems and questions.

On Monday 22 May 2006 13:26, Digby Tarvin wrote:
> On Sat, May 20, 2006 at 09:45:02PM +0300, David Baron wrote:
> > This is the "print" from fdisk from my linux disk:
> >
> > Disk /dev/hdc: 41.1 GB, 41110142976 bytes
> > 16 heads, 63 sectors/track, 79656 cylinders
> > Units = cylinders of 1008 * 512 = 516096 bytes
> >
> >    Device Boot      Start         End      Blocks   Id  System
> > /dev/hdc1   *       65520       77600     6088635   83  Linux
> > /dev/hdc2               1       65519    33021544+   f  W95 Ext'd (LBA)
> > /dev/hdc3           77600       79640     1028160   82  Linux swap /
> > Solaris /dev/hdc5               1       38753    19531449    b  W95 FAT32
> > /dev/hdc6           38753       46504     3906250+  83  Linux
> > /dev/hdc7           46504       52704     3125000+  83  Linux
> > /dev/hdc8           52704       56579     1953125+  83  Linux
> > /dev/hdc9           56580       60455     1953125+  83  Linux
> > /dev/hdc10          60455       65519     2552603   83  Linux
> >
> > Partition table entries are not in disk order
> >
> > The disk orginally had another large vfat partition which as removed and
> > more ext3 partitions placed which is why they are in this "order".
> >
> > When I first partitioned the disk and after I repartitioned it, the
> > partitions were all 100% legal. They read into parted, qtparted,
> > partitionmagic, etc. no problem. After a while (and I have had this
> > problem a long time now), parted would no longer accept the disk.
> > Complains of overlapping cylinder boundaries. Partitionmagic just calls
> > is "bad". Obviously, I have been using these partitions without problems.
> >
> > Since I have a lot of extra space on my other disk (windows which I use
> > much less now), I would like to make changes. First to fix this up. So.
> >
> > 1. How might I re-legalize the above partition table without starting
> > over, obviously.
> > 2. Is it better to have swap on a different disk (and IDE)--this is one
> > of the changes I am thinking of?
> >
> > Thanks for any advice.
> I haven't seen anyone else respond to this yet, so I will have a go...
> The partition table format used on PC is old and clumsy, with plenty of
> scope for redundent/conflicting information such that you can end up
> with some partitioning programs producing things that other
> partitioners or operatating systems object to...
> Two common sources of problem I have found are partition tables that
> are not in the same order in the table as the partitions are on disk,
> and the location and size of the extended partition in the primary
> partition table (some systems require the extended partition to be
> the last primary partition, others will create and use it anywhere)

Yes, this one is out of order, but when first done, it read into both 
partitionmagic from the window and parted from linux 100%. Somewhere along 
the line, the problem was produced.

> The good news is that providing you keep the phyical start and end
> addressed partitions the same, you can generally get away with removing
> and rewriting the partition table without losing your partition contents.
> I have done this several times, recently when one of the more modern
> partitioners decided to shrink my 'extended' partition to match the
> total of the sizes of the partitions initially created within - rather
> than leave it using the rest of the space on the media. This meant that
> even though I was ony using about a third of the disk, I could not create
> any additional partitions after completing the install because the
> extended partition was full...
> The procedure I used to fix this was to print a hardcopy of the output of
> 	'fdisk -l /dev/thedisk'
> Then I delete all of the logical partitions using fdisk, then
> delete the extended partition, recreate the extended partition
> with the correct size, and finally add logical partitions with
> exactly the same start and end cylinder numbers as the originals,
> in the correct order. Remember that the logical partitions are stored
> in a list, so if you delete a middle one, all the subsequent ones may
> disappear as well (at least with a dumb partitioner).
> To re-order your primary partitions, delete and recreate those
> as well. However I would be prepared to re-install your MBR if you recreate
> the first partition, depending on the partitioning program you are
> using.
> When finished, list the partition information and verify that
> the start and end cylinders really do exactly match the original
> values for the partitions you are retaining.
> Finally save the table (ignoring the warning about all data being
> destroyed on changed partitions), reboot to ensure the updated
> partition table has been read, and check your filesystems to
> confirm that all data is still there.
> In your case you appear to have gotten your logical partitions
> at the start of the disk, with your extended partition in the
> middle of your primary partition table, which would be a real
> torture test for most partitioners, and is a testament to the
> flexability of the Linux drivers that they can accept it.
> I'd probably make the FAT32 partition your hdc1, then create
> an extended partition for the rest, and add entries for each
> partition in order. But hdc6 and hdc7 could be made primary
> partitions also if desired.
> If it doesn't work, you should be able to boot from a CD or floppy
> and restore the partition table to its original state, as the
> partitions themselves are not changed by modifying the table.
> Of course I would never advise doing such a procedure unless everything
> valuable had been backed up first - just in case.

This procedure (yes, back it all up!) is not for the faint of heart. The 
"first" partition is my linux / so I would probably want to keep it that way. 
The FAT is Cakewalk audio data, generally not used in Linux since WINE will 
not run recent Cakewalk software. Rarely gets mounted.

I am a bit afraid to start with this but might get up the guts.

> If all else fails, the save way of doing this would be to just create
> identically sized partitions on another disk and dd stuff across.
> Then repartition the old drive from scratch.

> Regarding the swap partition - I think the main idea is to distribute
> the load. If you do a lot of swapping, then put the swap partition
> on the drive with the least accessed partitions. Alternatively,
> allocate a swap partition on each drive, and let the system
> spread the load.

How does one use multiple swaps? Simply place two in fstab?

I might just settle for making a new big home ext3 and a second swap on the 
"Windows" drive for now.

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