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Old 04-12-2012, 05:37 PM
Emmanuel Noobadmin
 
Default Installing CentOS 6.2 *TO* a USB drive, not installing from USB.

On 4/10/12, Phil Schaffner <Philip.R.Schaffner@nasa.gov> wrote:
> Have you tried the grub "find" command?
> find /grub/stage1
> find /boot/grub/stage1
> etc.
>
> http://wiki.centos.org/TipsAndTricks/TroubleshootGRUB

I've tried that now but it could not find any of the files be it
stage1, grub.conf or menu.lst, also tried both /grub and /boot/grub
variants.

The interesting thing is that if I leave the DVD in the DVDROM drive,
grub will find it as hd111 with the tab button. So the tab
functionality is actually working. Just that as far as grub is
concerned, the flash drive it just loaded from just seem to be
undetectable.
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Old 04-12-2012, 08:02 PM
Emmanuel Noobadmin
 
Default Installing CentOS 6.2 *TO* a USB drive, not installing from USB.

On a random hunch or sheer desperation, I inserted an old brandless
1GB USB thumbdrive, installed and it booted.

Thinking that the Sandisk Ultra Backup 16GB was incompatible with
CentOS/grub for some unknown reason. I switched to a brandless 16GB,
installed the same way and it failed at grub prompt again.

Now it is starting to look as if either the newer drives have
something on them that prevents booting. Or it's the total size of the
drive, regardless of the partition size. I say this because in every
case I used a single 1GB ext4 / partition for testing, to reduce the
mkfs time.

Since now I have a bootable drive, I started to compare them with
fdisk to see if there was any difference.

Bootable
255 heads, 63 sectors/track, 124 cylinders, start sector 63
With a warning that
"Partition 1 has different physical/logical endings:
phys=(123, 254, 63) logical=(124, 140, 16)"

Unbootable 16GB Sandisk Ultra Backup
54 heads, 48 sectors/track, 12158 cylinders, start sector 2048

Unbootable 8GB Sandisk Blade
20 heads, 4 sectors/track, 195417 cylinders, start sector 2048

Unbootable 16GB Unbranded
171 heads, 40 sectors/track, 4634 cylinders, start sector 2048

It seems that the common issue is starting at sector 2048 so I fdisk
the 16GB Sandisk to manually create a 1GB partition started at sector
63. Using this, I installed and was able to boot successfully.

To verify, I use the same 16GB disk to install again, deleting the
partition in anaconda and creating a new 1GB partition, ctrl-alt-f2
and fdisk confirms it was again at sector 2048.

As a side note, for some reason, drive geometry changed for the 16GB
after a reinsert to varying values such as
6 heads, 33 sectors/track, 159164 cylinders
16 heads, 32 sectors/track, 61551 cylinders

Not sure if this had any significance to why anaconda decides to fdisk
the drive starting from sector 2048.

My only guess is that it considers anything bigger than 4GB as a
normal HDD drive and does this for hard disk alignment issue? But if
grub could boot normally from such a HDD, why would it choke on a USB
flash drive?

Should I report this as a bug with anaconda or ?
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Old 04-12-2012, 08:55 PM
 
Default Installing CentOS 6.2 *TO* a USB drive, not installing from USB.

Emmanuel Noobadmin wrote:
> On a random hunch or sheer desperation, I inserted an old brandless
> 1GB USB thumbdrive, installed and it booted.
>
> Thinking that the Sandisk Ultra Backup 16GB was incompatible with
> CentOS/grub for some unknown reason. I switched to a brandless 16GB,
> installed the same way and it failed at grub prompt again.
>
> Now it is starting to look as if either the newer drives have
> something on them that prevents booting. Or it's the total size of the
> drive, regardless of the partition size. I say this because in every
> case I used a single 1GB ext4 / partition for testing, to reduce the
> mkfs time.
>
<snip>
>
> It seems that the common issue is starting at sector 2048 so I fdisk
> the 16GB Sandisk to manually create a 1GB partition started at sector
> 63. Using this, I installed and was able to boot successfully.
>
> To verify, I use the same 16GB disk to install again, deleting the
> partition in anaconda and creating a new 1GB partition, ctrl-alt-f2
> and fdisk confirms it was again at sector 2048.
>
> As a side note, for some reason, drive geometry changed for the 16GB
> after a reinsert to varying values such as
> 6 heads, 33 sectors/track, 159164 cylinders
> 16 heads, 32 sectors/track, 61551 cylinders
>
> Not sure if this had any significance to why anaconda decides to fdisk
> the drive starting from sector 2048.

Wonder if it's trying to beat the rush - after weeks of googling, a few
weeks ago, I finally found that if I formatted my 3TB drives on a 4k
boundry, instead of a 512byte boundry, writes were literally about four
times faster, because that's the physical sector on the drives.

It may be trying to do the same, to take care of this invisibly.

Good catch on the USB drive business.

mark

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Old 04-13-2012, 04:52 AM
Emmanuel Noobadmin
 
Default Installing CentOS 6.2 *TO* a USB drive, not installing from USB.

On 4/13/12, m.roth@5-cent.us <m.roth@5-cent.us> wrote:

> Wonder if it's trying to beat the rush - after weeks of googling, a few
> weeks ago, I finally found that if I formatted my 3TB drives on a 4k
> boundry, instead of a 512byte boundry, writes were literally about four
> times faster, because that's the physical sector on the drives.
>
> It may be trying to do the same, to take care of this invisibly.

That is what I think the 2K first sector is supposed to do, align the
physical sector be it a 512 or 4K drive. But unfortunately, the check
for "is this a 4K HDD" appears to be naive.
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