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 USB BIOS 128GB size limit
post Jun 13 2010, 12:34 PM
Post #1
karyonix
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Thailand


I just discover the size limit of USB functionality of my computer BIOS while testing booting from USB hard disk.
When GRUB4DOS read data (through BIOS) beyond the limit it does not show any error message. It just give me corrupted data.
It take me whole day to find out the limit. It's 0x10000000 sectors = 128GB.
When my docking station (with 250GB or 640GB hard disk) is connected with SATA, GRUB4DOS can read data (through BIOS) beyond 128GB correctly.
Windows can access the data on whole disk when the docking station is connected with either USB or SATA, so I think it is not docking station's limit. It is BIOS' limit.

My motherboard is ASUS P5Q PRO (chipset Intel P45 ICH10R). It is not old.
It's a surprise to see this small USB size limit while SATA (on same motherboard) does not have the same limit.
This problem may affect other people too.


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post Jun 13 2010, 12:41 PM
Post #2
Icecube
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Belgium


Yes, it affects me too. My internal SATA drive also doesn't has the 128 GiB (137GB) limit.
Using PLoP for booting the USB drive solves the problem for me.
Elmar (developer of PLoP) told me that PLoP should support drives up to 2 Terabyte (MBR limit).


--------------------
Use Parted Magic for handling all partitioning task. Download Parted Magic 4.11.
Parted Magic and grub4dos iso emulation

Ultimate Boot CD V5 forum for features and suggestions. Download Ultimate Boot CD v5.0.2 with grub4dos support.

The Syslinux Project: Stable releases: download link. Last test builds: download link.
ISO booting capable MEMDISK
2 user(s) said "Thank you!" to Icecube for this fantastic post:
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post Jun 13 2010, 12:50 PM
Post #3
MedEvil
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Wow! Running into a 128GB problem with USB-Booting.
Sometimes i really wish, people would post here, what wonders they're creating. smile.gif


cheers.gif


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NaughtyPE - The Multimedia PE!
Requirements: WinBuilder080, XPSP2/W2k3SP1 source, Pentium CPU, 128MB RAM (256MB to use video players)
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post Jun 13 2010, 12:54 PM
Post #4
steve6375
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United Kingdom


Is this a BIOS limitiation or grub4dos? How can you tell?


--------------------
Steve

Try RMPrepUSB for partitioning, formatting and making bootable your USB Flash Drive under Windows (supports FAT16/FAT32/NTFS, MSDOS/FreeDOS/XP/Vista, boot as Hard disk or floppy disk).
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post Jun 13 2010, 01:03 PM
Post #5
Icecube
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Belgium


QUOTE (steve6375 @ Jun 13 2010, 02:54 PM) *
Is this a BIOS limitiation or grub4dos? How can you tell?

It is a BIOS limitation.
I discovered it some months ago, while testing Syslinux-4.00-preXX.
The Syslinux-4.00 branch has EXT4 support.
Syslinux didn't fully boot. The partition on which I installed Syslinux started at 126GiB. I could display some files and directories with the "ls" command of grub4dos on that partition. But grub4dos couldn't display the files in a certain subdirectory. When using the "cat" command, grub4dos couldn't display the contents of some files which did show up in the output of "ls". I also tried to display and read files with grub2, but it also couldn't read all files.
First I was suspecting, filesystem implementation bugs in Syslinux, Grub4dos and grub2 (EXT4 is relatively new), but When I attached the USB drive to qemu, all bootloaders did work.
CODE
qemu -boot c -hda /dev/sdf


--------------------
Use Parted Magic for handling all partitioning task. Download Parted Magic 4.11.
Parted Magic and grub4dos iso emulation

Ultimate Boot CD V5 forum for features and suggestions. Download Ultimate Boot CD v5.0.2 with grub4dos support.

The Syslinux Project: Stable releases: download link. Last test builds: download link.
ISO booting capable MEMDISK
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post Jun 13 2010, 01:28 PM
Post #6
karyonix
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Thailand


QUOTE (steve6375 @ Jun 13 2010, 07:54 PM) *
Is this a BIOS limitiation or grub4dos? How can you tell?
GRUB4DOS knows nothing about USB or SATA. It use BIOS to read disk.
When I detach USB cable, attach eSATA cable to docking station and computer, and reboot. GRUB4DOS can read the disk correctly to the last sector of my 640GB disk.
When connected with eSATA cable, the result of dd command in GRUB4DOS is the same as result of dd for Windows.
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post Jun 13 2010, 04:09 PM
Post #7
steve6375
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Thanks for replies. Must be USB BIOS issue. I thought perhaps may be a bug in grub4dos as grub4dos has to call the BIOS using Extended Int13h BIOS calls, but obviously not if grub4dos works on same pc but not as USB device.


--------------------
Steve

Try RMPrepUSB for partitioning, formatting and making bootable your USB Flash Drive under Windows (supports FAT16/FAT32/NTFS, MSDOS/FreeDOS/XP/Vista, boot as Hard disk or floppy disk).
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