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Old 25th February 2012, 08:00 AM
ToddAndMargo Offline
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dual boot advice requested

Hi All,

I am in the "thinking" phase of setting up a new system for a customer. I will be wanting to install XP on partition one and FC16 on partition two.

Am I correct, the best way to go about this is to install XP first and them install FC16 second? (I intend to install from the Xfce Live CD.) GRUB will then take care of the dual booting?

Any advice on the issue?

Many thanks,
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Old 25th February 2012, 10:24 AM
glennzo Online
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Re: dual boot advice requested

You are correct on all thoughts.
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Old 26th February 2012, 05:00 AM
ToddAndMargo Offline
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Re: dual boot advice requested

Originally Posted by glennzo View Post
You are correct on all thoughts.
Thanks you for the sanity check!

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Old 26th February 2012, 03:20 PM
DBelton Offline
Join Date: Aug 2009
Posts: 8,453
Re: dual boot advice requested

Yes, you are pretty much correct.

Here is what I did, though..

MANUALLY partition the drive, create a NEW MBR partition table. (I'll explain why in a minute)

Create your Windows XP partition, (It should be the first PRIMARY partition on the drive.) and make sure to start it in sector 2048. (This is the reason for manually partitioning the drive and I will explain more about it in a minute)

This XP partition should be the size you want XP to be, and make sure you leave enough free space after it for your Fedora install.

Install Windows XP as you normally would, making sure to reboot get things set up right...

Now, it's easier for me to just manually set up the Fedora partitions myself, but you can let the Fedora installer do it if your wish. Just remember that you are limited to 4 PRIMARY partitions, so if you need more than 4 total partitions, then one of your primary ones has to be set up as an extended partition so you can create more inside of it.

Install Fedora as normal.. It should pick up your Windows install and add it to the grub menu for you, but there were some cases where the version of grub on the install media didn't pick it up correctly. If that happens, make sure that 0s-prober is installed, update grub, then run grub2-mkconfig -o /boot/grub2/grub.cfg as root.

Now for the reasons to manually set up the partitons and make sure you start the first one in sector 2048.

Windpws XP, if you have it format the drive and set it up, would start the first sector in sector 63. In a lot of cases, that does NOT leave enough space to insert the grub2 core.img file. The default formatting would give you approx 30kb between the MBR and the first parttion, and grub2's core.img file runs about 34kb on a system without RAID, or any other special modules that need to be loaded.

I ran into this issue after install F16 and had something mess up grub. When I went to re-install grub, it didn't have space for the core.img file. For some reason, the version of grub on the install media created a 29kb core.img file, and the updated grub created a 34kb core.img file. This was with the same grub configuration, same modules getting loaded, etc... Somthing in the updated grub version needed more space. I got lucky on mine that I had Fedora on my second hard drive that was a GPT drive, and I was able to insert a bios_boot partition on it, and boot from my second drive. If I had not been able to do that, I would have had to try and move partitions around on my XP drive and hope I didn't screw up the Windows install in the process.
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Old 26th February 2012, 08:49 PM
ToddAndMargo Offline
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Re: dual boot advice requested

Thank you!
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Old 27th February 2012, 06:03 AM
srs5694 Offline
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Re: dual boot advice requested

I'd not heard that the GRUB second-stage boot loader was now bigger than would fit in 61 sectors. That certainly wasn't a problem a year or two ago, but I suppose the code could have bloated since then....

Anyhow, there's another reason to do it as DBelton suggests: Most modern hard disks now use Advanced Format, in which the disk uses 4096-byte sectors but lies to the computer and claims it's got the more traditional sector size of 512 bytes. The trouble is that this can lead to severe performance degradation if partitions aren't properly aligned -- in some cases, write speeds can suffer by up to 25x, so that an operation that normally takes 1 second takes 25 seconds! (That's a worst-case scenario, though; most filesystems suffer by "only" about 2x.) To properly align partitions, they must begin on sector numbers that are multiples of 8. Since 63 is not such a multiple, and other partition start points selected by the Windows XP installer are not likely to be, either, you'll take a big performance hit if you let Windows XP partition an Advanced Format disk. 2048 is a multiple of 8, of course, so starting the first partition at sector 2048 is safe, and Fedora 16's partitioning tools will also start subsequent partitions on multiples of 2048 (and hence multiples of 8). If you use an old partitioning tool, such as a version of fdisk from more than a year or two ago, you may have to take care to align your partitions properly.

Of course, this is irrelevant if you're installing on an older hard disk, or even on a new one that doesn't use Advanced Format (if such beasts even exist any more; they might have gone extinct by now). Doing proper alignment for Advanced Format disks won't hurt on disks with true 512-byte sectors, so it's definitely safest to assume you've got an Advanced Format disk and align your partitions accordingly.
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