Re: [gentoo-user] migrating disks (from mounts to disklabels

[Mick]

On Saturday 20 November 2010 13:26:03 David W Noon wrote:
> On Sat, 20 Nov 2010 00:10:02 +0100, Mick wrote about Re: [gentoo-user]

> >Short of measuring the latency with some system (which I wouldn't know
> >how) I have experimented with setting the /boot partition on primary
> >and logical partitions and the difference (on a stopwatch) was
> >measurable in seconds betweeen having said partition on a primary and
> >having it on a logical. Furthermore, sda7 was slower than sda5.
>
> Unless you have the mother of all initrd's or initramfs's, you cannot
> have /boot on a logical partition -- only a primary partition, as BIOS
> interrupts will only access raw drives and primary partitions. If you do
> put /boot on a logical partition, you will pay the "lookup" overhead
> repeatedly as part of the early bootstrap process. Since you won't have
> a kernel running at that time. no caching, including device mapping,
> will be in force.  It will be dog slow if /boot is not in the primary
> partition table.

Thanks David, this explains then why booting from a logical partition takes 
longer.  After the GRUB code has run the OS loads normally, but that initial 
delay is explained by the lookup overhead (hence I thought that no much 
caching is happening at that stage). 

-- 
Regards,
Mick